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Stock-Based Compensation - Summary of Outstanding and Exercisable Incentive Options (RSUs and PSUs) (Detail)
12 Months Ended
Dec. 31, 2017
$ / shares
shares
Restricted Stock Units (RSUs) [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of incentive options, Outstanding, Beginning balance | shares 155,845
Number of incentive options, Granted | shares 76,473
Number of incentive options, Converted to common stock | shares (58,677)
Number of incentive options, Forfeited/cancelled | shares (14,935)
Number of incentive options, Outstanding, Ending balance | shares 158,706
Weighted Average Fair Value of incentive options, Outstanding, Beginning balance | $ / shares $ 17.53
Weighted Average Fair Value of incentive options, Granted | $ / shares 14.00
Weighted Average Fair Value of incentive options, Converted to common stock | $ / shares 17.25
Weighted Average Fair Value of incentive options, Forfeited/cancelled | $ / shares 16.76
Weighted Average Fair Value of incentive options, Outstanding, Ending Balance | $ / shares $ 16.00
Performance-based Restricted Stock Units (PSUs) [Member]  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of incentive options, Outstanding, Beginning balance | shares 39,348
Number of incentive options, Granted | shares 97,788
Number of incentive options, Converted to common stock | shares 0
Number of incentive options, Forfeited/cancelled | shares (34,622)
Number of incentive options, Outstanding, Ending balance | shares 102,514
Weighted Average Fair Value of incentive options, Outstanding, Beginning balance | $ / shares $ 21.62
Weighted Average Fair Value of incentive options, Granted | $ / shares 14.93
Weighted Average Fair Value of incentive options, Converted to common stock | $ / shares 0
Weighted Average Fair Value of incentive options, Forfeited/cancelled | $ / shares 14.99
Weighted Average Fair Value of incentive options, Outstanding, Ending Balance | $ / shares $ 17.47