Issuances of Common Stock - Dividend Reinvestment and Stock Purchase Plan (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		100 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019
Dividend Reinvestment and Stock Purchase Plan
Proceeds from dividend reinvestment and stock purchase plan			$ 4,098	$ 4,806
Common stock | Dividend Reinvestment and Stock Purchase Plan
Dividend Reinvestment and Stock Purchase Plan
Authorized common shares to be issued (in shares)			26,000,000
Share issuances (in shares)	27,520	47,128	59,418	93,061	14,289,228
Proceeds from dividend reinvestment and stock purchase plan	$ 1,900	$ 2,500	$ 4,100	$ 4,800	$ 675,000