Equity - Dividend Reinvestment and Stock Purchase Plan (Details) - USD ($) $ in Thousands	6 Months Ended		76 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017
Dividend Reinvestment and Stock Purchase Plan
Proceeds from dividend reinvestment and stock purchase plan	$ 59,649	$ 5,806
Common stock
Dividend Reinvestment and Stock Purchase Plan
Authorized common shares to be issued	26,000,000
Number of common shares issued	1,013,412	98,585	13,883,301
Proceeds from dividend reinvestment and stock purchase plan	$ 59,600	$ 5,800	$ 651,500
Number of common shares issued under the waiver approval process	927,695
Amount raised from share issued under the waiver approval process	$ 54,700