Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Statement of Other Comprehensive Income [Abstract]
Tax provision on unrealized gain on marketable securities	$ 0	$ (3)	$ 0	$ (5)
Tax benefit (provision) of unrealized loss on interest rate swap	(4,622)	4,273	(4,614)	4,566
Tax provision of reclassification adjustment	$ 1,020	$ 1,076	$ 2,045	$ 2,210