Statements Of Changes In Net Assets (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net income:
Net investment income	$ 190,919	$ 60,022	$ 34,051
Net realized gain (loss) on investments	35,756	6,115	(48)
Net unrealized appreciation (depreciation) on investments	(225,660)	4,832	(39,561)
Net gain (loss) from swap and cap contracts	(160,402)	(38,915)	(9,718)
Net income	291,933	22,390	63,846
Capital transactions:
Net proceeds from issuance of common shares	275,898	488,951	106,553
Distributions to shareholders	(162,455)	(29,861)	(6,002)
Tax return of capital distributions	(23,520)	(36,891)	(19,892)
Amortization of share based compensation	5,263	1,459	985
Increase in net assets from capital transactions	95,186	423,658	81,644
Total increase in net assets	387,119	446,048	145,490
Net assets:
Beginning of year	690,339	244,291	98,801
End of year	$ 1,077,458	$ 690,339	$ 244,291