Subsequent Events - Continuous Equity Offering Program (Details) - USD ($) $ / shares in Units, shares in Millions		3 Months Ended
	May 06, 2019	Mar. 31, 2019	Apr. 15, 2019	Sep. 19, 2016
Subsequent Event [Line Items]
Issuance of Common Stock, net		$ 27,544,000
Common Stock [Member]
Subsequent Event [Line Items]
Distribution agreement gross sales price (up to)				$ 750,000,000.0
Common Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Distribution agreement gross sales price (up to)			$ 750,000,000.0
Continuous Equity Offering Program [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Issuance of Common Stock, net (shares)		3.3
Issuance of Common Stock, net		$ 28,000,000.0
Proceeds from issuance of common stock		$ 27,500,000
Continuous Equity Offering Program [Member] | Common Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Issuance of Common Stock, net (shares)	5.0
Issuance of Common Stock, net	$ 42,500,000
Proceeds from issuance of common stock	$ 41,800,000
Weighted Average [Member] | Continuous Equity Offering Program [Member] | Common Stock [Member]
Subsequent Event [Line Items]
Share price (in dollars per share)		$ 8.46
Share price net of offering costs (in dollars per share)		$ 8.33
Weighted Average [Member] | Continuous Equity Offering Program [Member] | Common Stock [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Share price (in dollars per share)	$ 8.42
Share price net of offering costs (in dollars per share)	$ 8.30