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Performance Awards - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2017
Sep. 30, 2016
Sep. 30, 2017
Sep. 30, 2016
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Unearned compensation $ 2,100   $ 2,100  
Performance Awards        
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Compensation expense (300) $ 200 400 $ 400
Unearned compensation $ 1,362 $ 1,200 $ 1,362 $ 1,200
2014 Equity Incentive Plan | Performance Awards        
Deferred Compensation Arrangement with Individual, Share-based Payments [Line Items]        
Performance period     3 years