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Stockholders' Equity and Stock-Based Compensation - Summary of Nonvested Restricted Stock Awards Activity (Detail)
12 Months Ended
Dec. 31, 2017
$ / shares
shares
Time-Based Restricted Stock Awards [Member]  
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]  
Unvested shares of restricted stock outstanding at beginning of period | shares 1,429,514
Restricted stock awards granted | shares 309,526
Restricted stock awards vested | shares (681,699)
Restricted stock awards forfeited | shares (168,661)
Unvested shares of restricted stock outstanding at end of period | shares 888,680
Unvested shares of restricted stock outstanding, Weighted Average Grant Date Fair Value, at beginning of period | $ / shares $ 20.56
Granted, Weighted-Average Grant Date Fair Value | $ / shares 60.00
Vested, Weighted-Average Grant Date Fair Value | $ / shares 6.67
Forfeited, Weighted-Average Grant Date Fair Value | $ / shares 35.20
Unvested shares of restricted stock outstanding, Weighted Average Grant Date Fair Value, at end of period | $ / shares $ 42.17
Market-Based Restricted Stock Awards [Member]  
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]  
Unvested shares of restricted stock outstanding at beginning of period | shares 738,425
Restricted stock awards granted | shares 314,021
Restricted stock awards vested | shares (1,014,429)
Restricted stock awards forfeited | shares (38,017)
Unvested shares of restricted stock outstanding, Weighted Average Grant Date Fair Value, at beginning of period | $ / shares $ 28.68
Granted, Weighted-Average Grant Date Fair Value | $ / shares 48.63
Vested, Weighted-Average Grant Date Fair Value | $ / shares 34.44
Forfeited, Weighted-Average Grant Date Fair Value | $ / shares $ 39.87