Income Taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Income tax expense	$ 26,898	$ 19,812	$ 50,868	$ 42,948
Effective tax rate	39.00%	42.00%	38.00%	43.00%
Federal statutory rate	35.00%	35.00%	35.00%	35.00%
State income tax expense	1,710	2,487	3,064	5,290
Tax expense related to uncertain tax positions including accrued interest	866	546	1,630	2,069
Tax benefit (expense) from decrease (increase) in valuation allowance	1,800	(107)	1,800	(492)
Adjustment to paid-in capital for excess tax benefits from share-based compensation			1,492
Decrease in current deferred income tax assets due to utilization of NOLs			50,000
Minimum [Member]
Net operating loss carryforwards, expiration year			2031
Maximum [Member]
Net operating loss carryforwards, expiration year			2032
Alternative Minimum Tax Credit [Member]
Tax credit carryforward	5,000		5,000
Federal [Member]
Net operating loss carryforwards	6,000		6,000
Foreign [Member]
Tax credit carryforward	$ 15,900		$ 15,900
Foreign [Member] | Minimum [Member]
Foreign tax credit carryforwards, expiration year			2014
Foreign [Member] | Maximum [Member]
Foreign tax credit carryforwards, expiration year			2022