Supplemental Financial Information - Supplemental Income Statement - Interest Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
453A interest	$ 2,555	$ 2,490	$ 4,639
Line of Credit interest and letters of credit fees	417	89	49
Credit Agreement interest	0	2,112	1,180
Interest on RCM6 Note Payable, related party	0	263	2,468
Other	52	112	66
Interest expense	$ 3,024	$ 5,066	$ 8,402