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, 2013
Jun. 30, 2012
Jun. 30, 2013
Jun. 30, 2012
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Aggregate number of shares of common stock that may be issued for awards pursuant to the 2011 plan 11,750,000   11,750,000    
Aggregate number of shares of common stock that may be issued pursuant to the terms of the 2007 plan     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 1,200,000  
Granted, Weighted Average Grant Date Fair Value (Per share) $ 28.46 $ 22.17 $ 29.41 $ 21.69  
Vesting period for restricted stock and restricted stock units     3 years    
Vested, shares 200,000 100,000 1,100,000 900,000  
Fair value of restricted stock, vested $ 6.8 $ 1.2 $ 31.1 $ 17.8  
Unrecognized compensation cost, related to unvested restricted stock, total 37.9   37.9    
Expected weighted average period to recognize compensation cost on restricted stock (in years)     2 years 1 month 6 days    
Restricted Stock and Restricted Stock Units to be Settled in Common Stock [Member] | Former Executive Chairman [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Compensation cost associated with the accelerated vesting of restricted stock and RSUs 4.3   4.3    
Restricted Stock Units to be Settled in Cash [Member]
         
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting period for restricted stock and restricted stock units     3 years    
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 0.5 0.5 1.1 0.8  
Payment to settle liabilities under compensation plan     0.6 0.3  
Liabilities under Compensation Plan $ 1.3   $ 1.3   $ 0.8