Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation Plans - Outstanding Awards Under 2013 Omnibus Equity Incentive Plan (Detail)

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Stock-Based Compensation Plans - Outstanding Awards Under 2013 Omnibus Equity Incentive Plan (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 1 Months Ended 3 Months Ended
Mar. 31, 2018
Feb. 28, 2018
Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Nonvested shares at December 31, 2017     981,855
Granted 15,000 126,712 141,712
Vested     (258,930)
Transferred     0
Forfeited/canceled     (6,558)
Nonvested shares at March 31, 2018 858,079   858,079
Unrecognized stock-based compensation expense as of March 31, 2018 $ 23,246   $ 23,246
Unrecognized stock-based compensation expenses recognition period     3 years 1 month 20 days
Nonvested weighted average grant date fair value per share, beginning balance     $ 23.90
Weighted average grant date fair value per share, Granted     32.43
Weighted average grant date fair value, Vested     20.59
Weighted average grant date fair value, Transferred     0
Weighted average grant date fair value, Forfeited/canceled     29.21
Nonvested weighted average grant date fair value per share, ending balance $ 26.27   $ 26.27
Restricted Stock Awards [Member] | Non-Employee Directors [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Nonvested shares at December 31, 2017     30,732
Granted 0 0 0
Vested     0
Transferred     0
Forfeited/canceled     0
Nonvested shares at March 31, 2018 30,732   30,732
Unrecognized stock-based compensation expense as of March 31, 2018 $ 423   $ 423
Unrecognized stock-based compensation expenses recognition period     1 year 7 months 6 days
Restricted Stock Units [Member] | Employees [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Nonvested shares at December 31, 2017     500,859
Granted 15,000 106,419 121,419
Vested     (132,325)
Transferred     0
Forfeited/canceled     (1,960)
Nonvested shares at March 31, 2018 487,993   487,993
Unrecognized stock-based compensation expense as of March 31, 2018 $ 12,669   $ 12,669
Unrecognized stock-based compensation expenses recognition period     3 years 6 months 14 days
Restricted Stock Units [Member] | Independent Contractors [member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Nonvested shares at December 31, 2017     450,264
Granted 0 20,293 20,293
Vested     (126,605)
Transferred     0
Forfeited/canceled     (4,598)
Nonvested shares at March 31, 2018 339,354   339,354
Unrecognized stock-based compensation expense as of March 31, 2018 $ 10,154   $ 10,154
Unrecognized stock-based compensation expenses recognition period     2 years 8 months 9 days