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Performance Awards - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]    
Unrecognized compensation expense $ 4.2  
Performance Awards    
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]    
Compensation expense 0.8 $ 0.3
Unrecognized compensation expense $ 2.2 $ 2.0
2014 Equity Incentive Plan | Performance Awards    
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]    
Performance period 3 years