Equity - Dividends on Common Stock (Details) - $ / shares	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Equity [Abstract]
Dividends declared per common share (in usd per share)	$ 0.185	$ 0.185	$ 0.185	$ 0.17	$ 0.555	$ 0.51	$ 0.68
Dividend, payable date	Oct. 13, 2017	Jul. 14, 2017	Apr. 14, 2017
Dividend, record date	Sep. 29, 2017	Jun. 30, 2017	Mar. 31, 2017