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Stock Based Compensation - Summary of Restricted Stock and Restricted Stock Units (Detail) - Restricted Stock and Restricted Stock Units [Member] - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted Stock Beginning Balance, Shares 1,349 1,098 1,404
Granted 432 810 591
Restricted stock vested (482) (552) (781)
Forfeited (109) (7) (116)
Restricted Stock Ending Balance, Shares 1,190 1,349 1,098
Restricted stock units vested at December 31, 2017 134    
Restricted Stock Beginning Balance, Weighted Average Grant Date Fair Value $ 3.64 $ 3.16 $ 2.44
Granted, Weighted Average Grant Date Fair Value 6.77 3.94 3.24
Restricted stock vested, Weighted Average Grant Date Fair Value 3.62 2.75 2.03
Forfeited, Weighted Average Grant Date Fair Value 3.94 3.28 3.45
Restricted Stock Ending Balance, Weighted Average Grant Date Fair Value 4.75 $ 3.64 $ 3.16
Restricted stock units vested, Weighted Average Grant Date Fair Value $ 2.56    
Restricted Outstanding, Aggregate Intrinsic Value $ 7,913    
Restricted stock units vested, Aggregate Intrinsic Value $ 888    
Restricted Stock Outstanding, Average Remaining Vesting Period (months) 14 months 9 days    
Restricted Stock Outstanding, Unrecognized Compensation Expense $ 3,335