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Stock-Based Compensation - Additional Information (Detail) (USD $)
 12 Months Ended 1 Months Ended 12 Months Ended 12 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2012
Y
Dec. 31, 2011
Dec. 31, 2010
Mar. 31, 2010
Class C common unit interests [Member]
Dec. 31, 2012
Class C common unit interests [Member]
Dec. 31, 2012
Performance Share Unit Awards [Member]
Jul. 30, 2012
Performance Share Unit Awards [Member]
Dec. 31, 2012
Performance Share Unit Awards [Member]
Minimum [Member]
Dec. 31, 2012
Performance Share Unit Awards [Member]
Maximum [Member]
Dec. 31, 2010
Discretionary stock awards [Member]
Dec. 31, 2012
Discretionary stock awards [Member]
Dec. 31, 2011
Discretionary stock awards [Member]
Dec. 31, 2010
Discretionary stock awards [Member]
Class C common unit interests [Member]
Dec. 31, 2012
Restricted stock awards [Member]
Dec. 31, 2011
Restricted stock awards [Member]
Dec. 31, 2010
Restricted stock awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                                
Stock-based compensation expense $ 10,333,000 $ 3,656,000 $ 9,970,000     $ 400,000               $ 10,200,000 $ 3,700,000 $ 1,200,000
Unrecognized expense of outstanding PSUs           3,600,000               17,200,000    
Unrecognized expense recognition period, years 2 years 2 months 12 days         3 years 7 months 6 days                    
Fair value of awards vested 11,700,000                              
Right to received shares of common stock             1                  
Performance share units initial performance period, years 3                              
PSU granted percentage of earnings               0.00% 200.00%              
Amortized performance period           4 years                    
Number of trading days 30 days                              
Stock-based compensation expense recorded       $ 5,200,000 $ 0         $ 3,500,000 $ 0 $ 0 $ 8,700,000      
Common units granted in period 753,285 248,228   1,000,000   155,220                    
Percentage of fair value allocable       95.00%                        
Expected volatility rate       60.00%   51.00%                    
Risk-free interest rate       2.08%   0.46%                    
Expected liquidity term, years       4 years   4 years 2 days