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Stock-Based Compensation - Restricted Stock - Service-Based - Additional Information (Detail) - Service Based Restricted Stock [Member] - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Grants vesting period     4 years  
Restricted shares vested grant date intrinsic value $ 6.0 $ 13.0 $ 0.5 $ 1.5
Unrecognized compensation expense $ 4.4   $ 4.4  
Weighted average period     1 year 9 months 18 days