Stockholders' Equity of the Company - Schedule of Common Stock Issued and Proceeds Received Dividend Reinvestments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 28, 2015
Stockholders' Equity
Common stock, shares authorized	160,000,000	160,000,000
Dividend reinvestments/stock purchases under the DRSPP	$ 0	$ 0	$ 124,761
Dividend Reinvestment and Stock Purchase Plan (DRIP)
Stockholders' Equity
Common stock, shares authorized				3,500,000
Issuance of common stock (in shares)	2,141	2,687	775,760
Dividend reinvestments/stock purchases under the DRSPP	$ 223	$ 277	$ 99,555