Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Net income	$ 349,245	$ 284,373	$ 169,500
Other comprehensive income (loss):
Net unrealized gains (losses) on securities available for sale	115,008	223,333	(34,898)
Net unrealized (losses) gains on derivative instruments	(25,476)	(155,902)	(11,934)
Other comprehensive income (loss)	89,532	67,431	(46,832)
Comprehensive income	$ 438,777	$ 351,804	$ 122,668