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Stock-based Compensation - Summary of Restricted Stock Units (Detail)
9 Months Ended
Sep. 30, 2017
$ / shares
shares
Time-Based Restricted Stock Units [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Number of Shares, Outstanding, Beginning Balance | shares 691,952
Number of Shares, Granted | shares 184,370
Number of Shares, Vested | shares (370,331)
Number of Shares, Forfeited or expired | shares (4,559)
Number of Shares, Outstanding, Ending Balance | shares 501,432
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares $ 8.28
Weighted-Average Grant Date Fair Value, Granted | $ / shares 10.05
Weighted-Average Grant Date Fair Value, Vested | $ / shares 7.15
Weighted-Average Grant Date Fair Value, Forfeited or expired | $ / shares 8.78
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares $ 9.76
Performance-Based Restricted Stock Units [Member]  
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]  
Number of Shares, Outstanding, Beginning Balance | shares 473,608
Number of Shares, Vested | shares (214,835)
Number of Shares, Forfeited or expired | shares (40,174)
Number of Shares, Outstanding, Ending Balance | shares 218,599
Weighted-Average Exercise Price, Outstanding, Beginning Balance | $ / shares $ 7.80
Weighted-Average Grant Date Fair Value, Vested | $ / shares 6.78
Weighted-Average Grant Date Fair Value, Forfeited or expired | $ / shares 7.01
Weighted-Average Exercise Price, Outstanding, Ending Balance | $ / shares $ 7.80