Consolidated Statements of Comprehensive Income (Parenthetical) (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 Other Comprehensive Income [Abstract]
Tax provision on unrealized gain on marketable securities	$ 0	$ 10	$ 0	$ 5
Tax benefit (provision) of unrealized loss on interest rate swap	1,615	2,786	(2,999)	7,352
Tax provision of reclassification adjustment	$ 1,075	$ 1,006	$ 3,120	$ 3,216