CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
8.25% Series A preferred stock
Preferred stock, dividend rate (as a percent)	8.25%	8.25%	8.25%
7.75% Series B preferred stock
Preferred stock, dividend rate (as a percent)	7.75%	7.75%	7.75%
8.50% Series C preferred stock
Preferred stock, dividend rate (as a percent)	8.50%	8.50%