Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Consolidated Statements of Comprehensive Income [Abstract]
Net income	$ 35,790	$ 42,977
Net unrealized loss on derivative instruments arising during the period, net of tax	(3,770)	(21,848)
Reclassification adjustment for gain on derivative instruments included in net income, net of tax	2,329	230
Net unrealized loss on derivative instruments qualifying as hedges	(6,099)	(22,078)
Foreign currency translation adjustment, net of tax	144	211
Net unrealized gains on available-for-sale investments, net of tax	26	16
Other comprehensive income	(5,929)	(21,851)
Comprehensive income	29,861	21,126
Other comprehensive income (loss), Parenthetical [Abstract]
Net unrealized loss on derivative instruments arising during the period, tax	(2,225)	(13,109)
Reclassification adjustment for gain on derivative instruments included in net income, tax	1,366	137
Foreign currency translation adjustment, tax	138	137
Net unrealized gains on available-for-sale investments, tax	$ 14	$ 9