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Stock-based Compensation - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2015
Jun. 30, 2014
Jun. 30, 2015
Jun. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares of common stock reserved for issuance 1,800,000   1,800,000  
Shares of common stock available for issuance 343,451   343,451  
Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Cash used for employee withholding tax payments     $ 4.8 $ 9.3
Share settlement under RSUs     35,486 49,819
Unamortized stock-based compensation expense $ 17.2   $ 17.2  
Weighted-average remaining amortization period     1 year 10 months 24 days  
Stock Options [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Contractual life in years     10 years  
Vesting period of stock options in years     3 years  
Stock-based compensation expense $ 3.4 $ 2.9 $ 6.4 $ 4.5
RSU and Performance Shares [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Company granted performance contingent RSU     33,632 30,101
Stock-based compensation expense     $ 1.2 $ 0.5
Minimum [Member] | Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Contractual life in years     1 year  
Maximum [Member] | Restricted Stock Units (RSUs) [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Contractual life in years     3 years