Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified					12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2012 Series A Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series A Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series E Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series F Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series G Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series G Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2012 Series H Cumulative Redeemable Preferred Stock [Member]	Dec. 31, 2011 Series H Cumulative Redeemable Preferred Stock [Member]
VIE Asset Amount	$ 337,000		$ 108,500
Common stock, par value	$ 0.01		$ 0.01
Common stock, shares authorized	150,000,000		150,000,000
Common stock, shares issued	74,926,981		58,819,717
Common stock, shares outstanding	74,926,981	[1]	58,819,717	[1]
Preferred stock, shares authorized	30,000,000		30,000,000			1,500,000		1,610,000		3,450,000	4,600,000		4,000,000
Preferred stock, par value	$ 0.01		$ 0.01			$ 0.01		$ 0.01		$ 0.01	$ 0.01		$ 0.01
Preferred stock, shares issued						0		1,610,000		3,450,000	4,000,000		4,000,000
Preferred stock, shares outstanding						0		1,610,000		3,450,000	4,000,000		4,000,000
Preferred stock dividend rate percentage						7.45%		7.80%		7.50%	6.875%		6.375%
Preferred stock liquidation preference								$ 40,250		$ 86,250	$ 100,000		$ 100,000

[1] The amount includes nonvested shares.