Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Series D Depositary Share [Member]
Series C preferred stock, per share	$ 0.53776	$ 1.84375	$ 1.84375
Series D preferred stock, per share		$ 1.84375	$ 1.84375	$ 1.34340
Common stock, per share	$ 1.56	$ 1.53	$ 1.51
Stock issued during period, shares	40,460	17,288,265	39,872	11,500,000
ATM equity program, shares	4,282,298
Discounted stock purchase program, shares	1,689,160	3,197,127	491,705
Restricted common stock, shares	373,913	133,432	377,164