Quarterly report pursuant to Section 13 or 15(d)

Investments in Marketable Securities - Schedule of Amortized Cost and Fair Value of Marketable Securities, Available-for-Sale, by Contractual Maturity (Detail)

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Investments in Marketable Securities - Schedule of Amortized Cost and Fair Value of Marketable Securities, Available-for-Sale, by Contractual Maturity (Detail) - USD ($)
$ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2015
Dec. 31, 2014
Investments, Debt and Equity Securities [Abstract]    
Due in one year or less, Amortized Cost $ 89,731  
Due after one year through five years, Amortized Cost 18,948 $ 4,679
Due after five years through ten years, Amortized Cost 17,835 5,652
Due after ten years, Amortized Cost 8,622 4,381
Amortized Cost 135,136 14,712
Due in one year or less, Fair Value 89,764  
Due after one year through five years, Fair Value 18,955 4,679
Due after five years through ten years, Fair Value 17,474 5,662
Due after ten years, Fair Value 8,575 4,411
Total Fair Value $ 134,768 $ 14,752
Weighted average maturity 3 years 4 months 24 days 9 years 7 months 6 days