Issuances of Common Stock - Dividend Reinvestment and Stock Purchase Plan (Details) - USD ($) $ in Thousands	3 Months Ended		97 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019
Dividend Reinvestment and Stock Purchase Plan
Proceeds from dividend reinvestment and stock purchase plan	$ 2,164	$ 2,346
Common stock distributions
Dividend Reinvestment and Stock Purchase Plan
Authorized common shares to be issued (in shares)	26,000,000
Number of common shares issued (in shares)	31,898	45,933	14,261,708
Proceeds from dividend reinvestment and stock purchase plan	$ 2,200	$ 2,300	$ 673,100