Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Series D Depositary Share	Dec. 31, 2013 Series E Depositary Share
Series C preferred stock, per share		$ 0.53776	$ 1.84375
Series D preferred stock, per share				$ 1.34340	$ 0.77188
Common stock, per share	$ 1.60	$ 1.56	$ 1.53
Stock issued during period, shares	29,013	40,460	17,288,265	11,500,000	11,500,000
ATM equity program, shares	6,956,992	4,282,298
Conversion of 2028 Notes, shares	2,407,911
Discounted stock purchase program, shares	322,084	1,689,160	3,197,127
Restricted common stock, shares	290,181	373,913	133,432