Quarterly report pursuant to Section 13 or 15(d)

Equity-Based Compensation - Additional Information (Detail)

v2.4.0.8
Equity-Based Compensation - Additional Information (Detail) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Dec. 31, 2013
2011 Plan [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Aggregate number of shares of common stock that may be issued 11,750,000   11,750,000    
2007 Plan [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Aggregate number of shares of common stock that may be issued 4,000,000   4,000,000    
Restricted Stock and Restricted Stock Units to be Settled in Common Stock [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Granted, shares 100,000 100,000 1,400,000 1,400,000  
Granted, weighted average grant date fair value, per share $ 33.31 $ 28.46 $ 35.11 $ 29.41  
Vested, shares 100,000 200,000 1,100,000 1,100,000  
Fair value of restricted stock, vested $ 3.5 $ 6.8 $ 37.0 $ 31.1  
Unrecognized compensation cost, related to unvested restricted stock, total 47.9   47.9    
Expected weighted average period to recognize compensation cost on restricted stock and RSUs to be settled in stock (in years)     2 years 4 days    
Restricted Stock and Restricted Stock Units to be Settled in Common Stock [Member] | Maximum [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period for restricted stock and restricted stock units     3 years    
Restricted Stock and Restricted Stock Units to be Settled in Common Stock [Member] | Minimum [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period for restricted stock and restricted stock units     2 years    
Restricted Stock Units to be Settled in Cash [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of common stock shares that may be received by RSU holder     1    
Compensation expense related to Restricted Stock Units to be settled in cash 0.9 0.5 1.6 1.1  
Payment to settle liabilities under compensation plan 0.1   2.2 0.6  
Accrued liabilities under Compensation Plan $ 1.5   $ 1.5   $ 2.1
Restricted Stock Units to be Settled in Cash [Member] | Maximum [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period for restricted stock and restricted stock units     3 years    
Restricted Stock Units to be Settled in Cash [Member] | Minimum [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period for restricted stock and restricted stock units     2 years