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Stockholders' Equity - Summary of Assumptions Used to Calculate the Grant Date Fair Value inducement Award (Detail) - 2016 Performance - Vesting Inducement Award
12 Months Ended
Dec. 31, 2017
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Payout Of Award for Projected Achievement of Target, Percent 0.00%
Fair value on grant date (in usd per share) $ 12.55
Expected price volatility, percent 24.60%
Risk-free interest rate 0.92%