Issuances of Common Stock - Dividend Reinvestment and Stock Purchase Plan (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Dividend Reinvestment and Stock Purchase Plan
Gross proceeds	$ 8,437	$ 9,114	$ 69,931
DRSPP
Dividend Reinvestment and Stock Purchase Plan
Common shares for future issuance (in shares)	26,000,000
Shares remaining for future issuance (in shares)	11,652,668
Common stock | DRSPP
Dividend Reinvestment and Stock Purchase Plan
Shares of common stock issued (in shares)	117,522	166,268	1,193,653
Gross proceeds	$ 8,400	$ 9,100	$ 69,900
Common stock | DRSPP, component related to waiver approval process
Dividend Reinvestment and Stock Purchase Plan
Shares of common stock issued (in shares)			927,695
Gross proceeds			$ 54,700