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 9 Months Ended
Aug. 31, 2017
May 31, 2017
Feb. 28, 2017
Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Nonvested shares at December 31, 2016       1,050,430
Granted 62,749 33,794 146,285 242,828
Vested       (288,011)
Transferred       0
Forfeited/canceled       (26,465)
Nonvested shares at September 30, 2017       978,782
Unrecognized stock-based compensation expense as of September 30, 2017       $ 20,360
Weighted average remaining vesting period (years) as of September 30, 2017       2 years 11 months 26 days
Nonvested weighted average grant date fair value per share, beginning balance       $ 22.38
Weighted average grant date fair value per share, Granted       26.69
Weighted average grant date fair value, Vested       20.99
Weighted average grant date fair value, Transferred       25.23
Weighted average grant date fair value, Forfeited/canceled       24.37
Nonvested weighted average grant date fair value per share, ending balance       $ 23.80
Restricted Stock Awards [Member] | Non-Employee Directors [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Nonvested shares at December 31, 2016       29,112
Granted 3,552 13,986 0 17,538
Vested       (15,918)
Transferred       0
Forfeited/canceled       0
Nonvested shares at September 30, 2017       30,732
Unrecognized stock-based compensation expense as of September 30, 2017       $ 647
Weighted average remaining vesting period (years) as of September 30, 2017       1 year 10 months 14 days
Restricted Stock Units [Member] | Employees [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Nonvested shares at December 31, 2016       566,480
Granted 7,889 8,156 139,013 155,058
Vested       (138,030)
Transferred       (33,961)
Forfeited/canceled       (23,600)
Nonvested shares at September 30, 2017       525,947
Unrecognized stock-based compensation expense as of September 30, 2017       $ 11,143
Weighted average remaining vesting period (years) as of September 30, 2017       3 years 3 months 8 days
Restricted Stock Units [Member] | Independent Contractors [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Nonvested shares at December 31, 2016       454,838
Granted 51,308 11,652 7,272 70,232
Vested       (134,063)
Transferred       33,961
Forfeited/canceled       (2,865)
Nonvested shares at September 30, 2017       422,103
Unrecognized stock-based compensation expense as of September 30, 2017       $ 8,570
Weighted average remaining vesting period (years) as of September 30, 2017       2 years 8 months 12 days