Consolidated Statements Of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Consolidated Statements Of Comprehensive Income [Abstract]
Net income	$ 160,204	$ 126,896	$ 129,263
Amounts related to available-for-sale securities:
Change in net unrealized gains	54,263	1,057	169,145
Reclassification adjustment for amounts included in net income	62
Amounts related to cash flow hedges:
Change in net unrealized losses	(51,751)	(27,587)	(16,709)
Reclassification adjustment for amounts included in net income	28,066	27,546	57,827
Other comprehensive income	30,640	1,016	210,263
Comprehensive income	$ 190,844	$ 127,912	$ 339,526