Noncontrolling Interests (Redeemable Preferred Units) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Net income	$ 0	$ 0	$ 6
Redemption of redeemable preferred units (Series Four Preferred Units)	$ 0	0	(633)
Redeemable Preferred Units [Member]
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Beginning Balance		$ 0	633
Net income			6
Distributions			(6)
Redemption of redeemable preferred units (Series Four Preferred Units)			(633)
Ending Balance			$ 0