Stockholders' Equity (Details) (USD $) In Thousands, except Share data	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011		Jun. 30, 2010
Series C preferred stock dividends	$ 1,696	$ 1,696	$ 3,392	[1]	$ 3,392	[1]
Series C preferred stock: per share Dividends			$ 0.9218	[1]	$ 0.9218	[1]
Common stock: Dividends			63,887		62,174
Common stock: Per share			$ 0.760		$ 0.750
Dividends declared			$ 0.385
Dividends payable	2011-08		2011-08
Dividends recorded			Jul. 29, 2011
Net proceeds			56,391		11,832
DRIP [Member]
Shares of common stock issued			2,284,335		561,107
Net proceeds			$ 56,447		$ 11,770

[1] The Series C preferred stock has no maturity date and will remain outstanding unless redeemed.