Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statement of Other Comprehensive Income [Abstract]
Net Income	$ 81,972	$ 71,993	$ 57,638
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign Currency Translation Adjustments	(534)	(609)	(2,170)
Change in unrealized gains and losses on interest rate swaps, net of tax	(1,820)	1,777	996
Total Other Comprehensive Income (Loss)	(2,354)	1,168	(1,174)
Comprehensive Income	$ 79,618	$ 73,161	$ 56,464