Stockholder's Equity (Details 2) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity Note [Abstract]
Preferred stock, shares outstanding, beginning balance (in shares)			14,370,060	25,875,000	25,875,000
Shares redeemed (in shares)			0	(11,500,000)
Preferred stock conversions (in shares)			(95)	0
Preferred stock, shares outstanding, ending balance (in shares)	14,369,965	14,375,000	14,369,965	14,375,000	14,370,060	25,875,000
Preferred stock, dividend rate, percentage			6.50%	6.50%	6.50%	6.50%
Preferred stock, dividend rate, shares redeemed			0.00%	6.50%
Preferred stock, dividend rate, shares converted			6.50%	0.00%
Preferred stock redemption charge	$ 0	$ 0	$ 0	$ 9,769