Equity - Dividend Reinvestment and Stock Purchase Plan (Details) - USD ($) $ in Thousands	9 Months Ended		79 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017
Dividend Reinvestment and Stock Purchase Plan
Proceeds from dividend reinvestment and stock purchase plan	$ 67,813	$ 8,174
Common stock
Dividend Reinvestment and Stock Purchase Plan
Authorized common shares to be issued	26,000,000
Number of common shares issued	1,155,883	133,432	14,025,772
Proceeds from dividend reinvestment and stock purchase plan	$ 67,800	$ 8,200	$ 659,700
Number of common shares issued under the waiver approval process	927,695
Amount raised from share issued under the waiver approval process	$ 54,700