Income Taxes - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Estimated Federal taxable income	$ 188,362	$ 79,056
Statutory federal income tax rate	35.00%
Effective tax rate	34.35%	37.65%	36.10%
Income tax expense reduction	9,154
Unrecognized tax benefits that would affect effective tax rate	26,159
Reversal of accrued interest on unrecognized tax benefits	4,116
Accrued interest on unrecognized tax benefits		2,076	573
Total accrued interest on unrecognized tax benefits	20,658	24,797
Reduction in unrecognized tax benefits	$ 4,236