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Stockholders' Equity - Summary of Unrecognized Compensation Cost for Non-vested Restricted Shares (Detail)
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unrecognized compensation costs of non-vested cash awards excluded $ 1.2
Weighted average remaining contractual life (in years) 1 year 2 months 12 days
Current liabilities $ 1.0
Non-current liabilities 1.0
Restricted Stock  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unrecognized Compensation Costs $ 21.0
Weighted Average to be recognized (in years) 1 year 3 months 18 days
Restricted Stock Units (RSUs)  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Unrecognized Compensation Costs $ 11.3
Weighted Average to be recognized (in years) 1 year 3 months 18 days