Consolidated Statements of Comprehensive Income (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 73,863	$ 66,533	$ 78,051	$ 69,973
Other comprehensive income (loss):
Foreign currency translation adjustments	392	(1,159)	(455)	(232)
Change in unrealized gains and losses on interest rate swaps, net of tax	(334)	994	(218)	1,204
Total other comprehensive income (loss)	58	(165)	(673)	972
Comprehensive income	$ 73,921	$ 66,368	$ 77,378	$ 70,945