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Stock-based Compensation - Summary of Activity for Non-voting Performance Units (Detail) - Non-Voting Performance Based Restricted Stock Units [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]    
Share unit, Beginning Balance (shares) 818,150  
Share unit, Granted (shares) 448,012  
Share unit, Forfeited (shares) (165,397)  
Share unit, Vested and released to participants (shares) 0  
Share unit, Ending Balance (shares) 1,100,765 818,150
Weighted Average Grant Fair Value, Beginning Balance (in USD per share) $ 18.60  
Weighted average grant date fair value, grants (in USD per share) 12.54  
Weighted Average Grants Date Fair Value, Forfeited (in USD per share) 31.33  
Weighted Average Grants Date Fair Value, Vested and released to participants (in USD per share) 0.00  
Weighted Average Grant Fair Value, Ending Balance (in USD per share) $ 13.23 $ 18.60
Remaining Average Contractual Life, Ending 1 year 11 months 27 days 1 year 2 months 12 days
Aggregate Value $ 14,564 $ 15,218