Equity - Class of Stock Disclosures - Common Stock and Shelf Registrations (Details) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Equity
Net proceeds	$ 14,578,000	$ 78,592,000
Common Stock
Equity
Number of shares repurchased	41,592	49,094
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
Compensation paid to sales agents	260,000
Reclassification of accumulated costs to additional paid in capital	49,000
Amount available under effective shelf registration statement	$ 185,162,000