Summary Of Quarterly Results Of Operations (Schedule Of Quarterly Results Of Operations) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary Of Quarterly Results Of Operations [Abstract]
Investment Income-Interest Income	$ 61,631	$ 64,566	$ 65,720	$ 40,980	$ 25,025	$ 16,312	$ 17,265	$ 16,937	$ 232,897	$ 75,539	$ 45,526
Total expenses	10,511	14,610	9,335	7,522	5,306	3,826	3,167	3,218	41,978	15,517	11,475
Net investment income	51,120	49,956	56,385	33,458	19,719	12,486	14,098	13,719	190,919	60,022	34,051
Net gain (loss) from investments	(8,588)	120,959	129,225	19,820	(66,125)	28,577	32,367	6,464	261,416	1,283	39,513
Net gain (loss) from swap and cap contracts	1,561	(74,594)	(86,188)	(1,181)	29,138	(39,153)	(18,860)	(10,040)	(160,402)	(38,915)	(9,718)
Net income (loss)	$ 44,093	$ 96,321	$ 99,422	$ 52,097	$ (17,268)	$ 1,910	$ 27,605	$ 10,143	$ 291,933	$ 22,390	$ 63,846
Net income (loss) per common share (diluted)	$ 0.53	$ 1.16	$ 1.20	$ 0.74	$ (0.38)	$ 0.05	$ 1.46	$ 0.54	$ 3.66	$ 0.73	$ 4.75