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Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Income Taxes [Line Items]      
U.S. federal tax statutory rate 35.00% 35.00% 35.00%
State income taxes, net of federal income tax benefit, Rate 2.47% 2.38% 2.75%
Pass-through loss prior to IPO not subject to federal tax, Rate       3.85%
Initial deferred tax expense, Rate       268.43%
Non-deductible stock-based compensation, Rate       10.08%
Annual effective tax expense, Total 37.62% 37.08% 323.83%
U.S. federal tax statutory rate, Amount $ 86,056 $ 44,163 $ 4,644
State income taxes, net of federal income tax benefit, Amount 6,068 3,004 364
Pass-through loss prior to IPO not subject to federal tax, Amount       511
Initial deferred tax expense, Amount       35,612
Non-deductible stock-based compensation, Amount       1,338
Annual effective tax expense, Amount 92,486 46,789 42,962
IPO [Member]
      
Income Taxes [Line Items]      
Non-deductible IPO costs and other, Rate 0.15% (0.30%) 3.72%
Non-deductible IPO costs and other, Amount $ 362 $ (378) $ 493