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 6 Months Ended
May 31, 2018
Mar. 31, 2018
Feb. 28, 2018
Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Nonvested shares at December 31, 2017       981,855
Granted 31,986 15,000 126,712 173,698
Vested       (287,676)
Transferred       0
Forfeited/canceled       (6,558)
Nonvested shares at June 30, 2018       861,319
Unrecognized stock-based compensation expense as of June 30, 2018       $ 22,249
Unrecognized stock-based compensation expenses recognition period       3 years 15 days
Nonvested weighted average grant date fair value per share, beginning balance       $ 23.90
Weighted average grant date fair value per share, Granted       32.90
Weighted average grant date fair value, Vested       21.13
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       $ 26.60
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 12,852 0 0 12,852
Vested       (12,936)
Transferred       0
Forfeited/canceled       0
Nonvested shares at June 30, 2018       30,648
Unrecognized stock-based compensation expense as of June 30, 2018       $ 708
Unrecognized stock-based compensation expenses recognition period       1 year 1 month 20 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 4,854 15,000 106,419 126,273
Vested       (138,229)
Transferred       0
Forfeited/canceled       (1,960)
Nonvested shares at June 30, 2018       486,943
Unrecognized stock-based compensation expense as of June 30, 2018       $ 11,743
Unrecognized stock-based compensation expenses recognition period       3 years 4 months 17 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 14,280 0 20,293 34,573
Vested       (136,511)
Transferred       0
Forfeited/canceled       (4,598)
Nonvested shares at June 30, 2018       343,728
Unrecognized stock-based compensation expense as of June 30, 2018       $ 9,798
Unrecognized stock-based compensation expenses recognition period       2 years 9 months 7 days