Related Party Arrangements - Issuance of Common Stock to the Advisor (Narrative) (Details) - USD ($) shares in Thousands, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019
Related Party Transaction [Line Items]
Issuance of common stock as payment for asset management fees					$ 5.0
Common Stock
Related Party Transaction [Line Items]
Share-based payment of advisor asset management fees (in shares)	352	352	294	294	700
Issuance of common stock as payment for asset management fees					$ 5.0