Annual report pursuant to Section 13 and 15(d)

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

v3.8.0.1
Stock-Based Compensation Plans - Outstanding Awards Under 2013 Omnibus Equity Incentive Plan (Detail) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
Nov. 30, 2017
Aug. 31, 2017
May 31, 2017
Feb. 28, 2017
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Nonvested shares at December 31, 2015         1,050,430 1,026,113
Granted 21,722 62,749 33,794 146,285 264,550 335,634
Vested         (295,597) (258,123)
Transferred         0 0
Forfeited/canceled         (37,528) (53,194)
Nonvested shares at December 31, 2016         981,855 1,050,430
Nonvested weighted average grant date fair value per share, beginning balance         $ 22.38 $ 21.17
Unrecognized stock-based compensation expense as of December 31, 2017         $ 20,317  
Weighted average grant date fair value per share, Granted         $ 26.86 23.76
Weighted average remaining vesting period (years) as of December 31, 2017         2 years 10 months 10 days  
Weighted average grant date fair value, Vested         $ 21.21 19.88
Weighted average grant date fair value, Transferred         25.70 14.54
Weighted average grant date fair value, Forfeited/canceled         23.30 20.07
Nonvested weighted average grant date fair value per share, ending balance         $ 23.90 $ 22.38
Restricted Stock Awards [Member] | Non-Employee Directors [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Nonvested shares at December 31, 2015         29,112 35,364
Granted 0 3,552 13,986 0 17,538 14,742
Vested         (15,918) (20,994)
Transferred         0 0
Forfeited/canceled         0 0
Nonvested shares at December 31, 2016         30,732 29,112
Unrecognized stock-based compensation expense as of December 31, 2017         $ 534  
Weighted average remaining vesting period (years) as of December 31, 2017         1 year 8 months 16 days  
Restricted Stock Units [Member] | Employees [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Nonvested shares at December 31, 2015         566,480 468,969
Granted 9,528 7,889 8,156 139,013 164,586 239,012
Vested         (140,480) (104,820)
Transferred         (58,503) 2,062
Forfeited/canceled         (31,224) (38,743)
Nonvested shares at December 31, 2016         500,859 566,480
Unrecognized stock-based compensation expense as of December 31, 2017         $ 9,753  
Weighted average remaining vesting period (years) as of December 31, 2017         3 years 1 month 16 days  
Restricted Stock Units [Member] | Independent Contractors [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Nonvested shares at December 31, 2015         454,838 521,780
Granted 12,194 51,308 11,652 7,272 82,426 81,880
Vested         (139,199) (132,309)
Transferred         58,503 (2,062)
Forfeited/canceled         (6,304) (14,451)
Nonvested shares at December 31, 2016         450,264 454,838
Unrecognized stock-based compensation expense as of December 31, 2017         $ 10,030  
Weighted average remaining vesting period (years) as of December 31, 2017         2 years 7 months 24 days