Equity Offerings (Details) - Distribution Agreement - USD ($) $ / shares in Units, shares in Thousands		12 Months Ended
	Nov. 03, 2017	Dec. 31, 2018	Dec. 31, 2017
Subsidiary, Sale of Stock [Line Items]
Maximum aggregate offering price	$ 125,000,000
Gross proceeds from sales of common stock		$ 40,300,000	$ 14,700,000
Issuance costs on sales of common stock		$ 700,000	$ 800,000
Number of shares sold		557	294
Price per share (in dollars per share)		$ 72.40	$ 49.85
Stock Available for Issuance		$ 70,000,000