CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Series A Preferred Stock
Preferred stock dividend rate (in dollars per share)	$ 1.74	$ 3.49	$ 3.48
Series B Preferred Stock
Preferred stock dividend rate (in dollars per share)	$ 2.91	$ 2.41	$ 2.06