Equity - Redemption of Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Apr. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Redemption of Preferred Stock
Excess of redemption value over carrying value of preferred shares subject to redemption		$ 0	$ 0	$ 0	$ 13,373
Class F Preferred Stock
Redemption of Preferred Stock
Preferred stock redeemed	16,350,000
Preferred stock, dividend rate (as a percent)	6.625%
Preferred stock, redemption price per share (in dollars per share)	$ 25
Excess of redemption value over carrying value of preferred shares subject to redemption					$ 13,400