| Investments in Marketable Securities (Tables)
 | 6 Months Ended | 
| Jun. 30, 2016 | 
|---|
| Investments, Debt and Equity Securities [Abstract] |  | 
| Schedule of Amortized Cost and Fair Value of Marketable Securities, Available-for-Sale, by Type of Security | 
 
 Amortized cost and fair value of marketable securities,
 available-for-sale, by type of security consisted of the following
 (in thousands): 
   
 
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 |  |  | June 30, 2016 |  |  | December 31, 2015 |  |  
 |  |  | Amortized Cost
 |  |  | Gross Unrealized
 Gains
 |  |  | Gross Unrealized
 Losses
 |  |  | Fair Value
 |  |  | Amortized Cost
 |  |  | Gross Unrealized
 Gains
 |  |  | Gross Unrealized
 Losses
 |  |  | Fair Value
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 Short-term investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
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 U.S. Treasuries |  | $ | 53,278 |  |  | $ | 35 |  |  | $ | — |  |  | $ | 53,313 |  |  | $ | 62,343 |  |  | $ | — |  |  | $ | (71 | ) |  | $ | 62,272 |  |  
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 U.S. Government Sponsored Entities |  |  | 8,509 |  |  |  | 7 |  |  |  | — |  |  |  | 8,516 |  |  |  | 17,571 |  |  |  | — |  |  |  | (12 | ) |  |  | 17,559 |  |  
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 Corporate debt securities |  |  | 19,939 |  |  |  | 7 |  |  |  | — |  |  |  | 19,946 |  |  |  | 29 |  |  |  | — |  |  |  | — |  |  |  | 29 |  |  
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 |  |  | $ | 81,726 |  |  | $ | 49 |  |  | $ | — |  |  | $ | 81,775 |  |  | $ | 79,943 |  |  | $ | — |  |  | $ | (83 | ) |  | $ | 79,860 |  |  
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 Long-term investments: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  
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 U.S. Treasuries |  | $ | 21,176 |  |  | $ | 250 |  |  | $ | — |  |  | $ | 21,426 |  |  | $ | 15,283 |  |  | $ | — |  |  | $ | (112 | ) |  | $ | 15,171 |  |  
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 U.S. Government Sponsored Entities |  |  | 15,919 |  |  |  | 48 |  |  |  | — |  |  |  | 15,967 |  |  |  | 12,107 |  |  |  | — |  |  |  | (85 | ) |  |  | 12,022 |  |  
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 Corporate debt securities |  |  | 16,412 |  |  |  | 503 |  |  |  | (39 | ) |  |  | 16,876 |  |  |  | 17,219 |  |  |  | 5 |  |  |  | (519 | ) |  |  | 16,705 |  |  
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 Asset-backed securities and other |  |  | 9,839 |  |  |  | 128 |  |  |  | (58 | ) |  |  | 9,909 |  |  |  | 10,649 |  |  |  | — |  |  |  | (152 | ) |  |  | 10,497 |  |  
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 |  |  | $ | 63,346 |  |  | $ | 929 |  |  | $ | (97 | ) |  | $ | 64,178 |  |  | $ | 55,258 |  |  | $ | 5 |  |  | $ | (868 | ) |  | $ | 54,395 |  |  
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| Amortized Cost and Fair Value of Investments in Available for Sale Securities | 
 
 The amortized cost and fair value of the Company’s
 investments in available-for-sale securities that have been in a
 continuous unrealized loss position consisted of the following (in
 thousands): 
   
 
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 |  |  | June 30, 2016 |  |  | December 31, 2015 |  |  
 |  |  | Unrealized Loss
 |  |  | Fair Value |  |  | Unrealized Loss
 |  |  | Fair Value |  |  
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 Less than 12 months |  | $ | (72 | ) |  | $ | 4,607 |  |  | $ | (951 | ) |  | $ | 129,117 |  |  
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 12 months or longer |  | $ | (25 | ) |  | $ | 1,879 |  |  | $ | — |  |  | $ | — |  |  
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| Gross Realized Gains and Losses from Sale of Available for Sale Securities | 
 
 Gross realized gains and gross realized losses from the sales of
 the Company’s available-for-sale securities consisted of the
 following (in thousands): 
   
 
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 |  |  | Three Months Ended June 30,
 |  |  | Six Months Ended June 30,
 |  |  
 |  |  | 2016 |  |  | 2015 |  |  | 2016 |  |  | 2015 |  |  
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 Gross realized gain (1) |  | $ | 20 |  |  | $ | 56 |  |  | $ | 20 |  |  | $ | 133 |  |  
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 Gross realized loss (1) |  | $ | — |  |  | $ | — |  |  | $ | (155 | ) |  | $ | (3 | ) |  
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 | (1) | Recorded in other income (expense),
 net in the condensed consolidated statements of net and
 comprehensive income. The cost basis of securities sold were
 determined on the specific identification method. |  | 
| Schedule of Amortized Cost and Fair Value of Marketable Securities, Available-for-Sale, by Contractual Maturity | 
 
 Amortized cost and fair value of marketable securities,
 available-for-sale, by contractual maturity consisted of the
 following (in thousands): 
   
 
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 |  |  | June 30, 2016 |  |  | December 31, 2015 |  |  
 |  |  | Amortized Cost
 |  |  | Fair Value |  |  | Amortized Cost
 |  |  | Fair Value |  |  
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 Due in one year or less |  | $ | 81,726 |  |  | $ | 81,775 |  |  | $ | 79,943 |  |  | $ | 79,860 |  |  
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 Due after one year through five years |  |  | 40,259 |  |  |  | 40,473 |  |  |  | 28,634 |  |  |  | 28,465 |  |  
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 Due after five years through ten years |  |  | 15,002 |  |  |  | 15,529 |  |  |  | 18,020 |  |  |  | 17,466 |  |  
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 Due after ten years |  |  | 8,085 |  |  |  | 8,176 |  |  |  | 8,604 |  |  |  | 8,464 |  |  
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 |  |  | $ | 145,072 |  |  | $ | 145,953 |  |  | $ | 135,201 |  |  | $ | 134,255 |  |  
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 Weighted average contractual maturity |  |  | 3.0 years |  |  |  |  |  |  |  | 3.3 years |  |  |  |  |  |  |