Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 32,332	$ 21,375	$ 102,305	$ 89,969
Other comprehensive income (loss):
Foreign currency translation adjustments	(128)	(135)	(361)	(466)
Change in unrealized gains and losses on interest rate swaps, net of tax	(291)	(635)	913	(1,970)
Total other comprehensive income (loss)	(419)	(770)	552	(2,436)
Comprehensive income	$ 31,913	$ 20,605	$ 102,857	$ 87,533