Equity - Class of Stock Disclosures - Common Stock and Shelf Registrations (Details) - USD ($)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Equity
Net proceeds		$ 14,578,000
Common Stock
Equity
Number of shares repurchased	30,839	41,592
Common Stock | Equity Distribution Agreements
Equity
Maximum offering capacity under shelf registration statement	$ 200,000,000
Shares common stock sold		312,881
Net proceeds		$ 14,578,000
Amount available under effective shelf registration statement	$ 185,162,000	$ 185,162,000