Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Common stock (in dollars per share)	$ 1.71	$ 1.65	$ 1.60
Stock issued during period, shares	34,230	5,493,595	29,013
ATM equity program, shares	8,573,533	3,758,362	6,956,992
Conversion of 2028 Notes, shares			2,407,911
Discounted stock purchase program, shares	12,065	100,161	322,084
Restricted common stock, shares	209,284	360,808	290,181
Series D Depositary Share
Series D preferred stock (in dollars per share)	$ 1.65625	$ 1.65625	$ 1.65625
Series E Depositary Share
Series D preferred stock (in dollars per share)	$ 1.42500	$ 1.42500	$ 0.77188
Stock issued during period, shares			11,500,000