Equity - ATM Offering (Details) - USD ($) $ / shares in Units, shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2018	Jun. 30, 2017
Class of Stock [Line Items]
Remaining offering amount available	$ 187,900,000		$ 187,900,000
Gross proceeds			47,547,000	$ 170,485,000
Commissions paid on stock issuance			$ 600,000
At-The-Market Offering
Class of Stock [Line Items]
Number of shares (in shares)	2,989	0	2,989
Average sales price per share (in usd per share)	$ 16.13	$ 0.00	$ 16.13
Gross proceeds	$ 48,198,000	$ 0	$ 48,198,000
At-The-Market Offering | Maximum
Class of Stock [Line Items]
Authorized aggregate offering price of common stock				$ 300,000,000.0