Income Taxes - Components of the company's income tax (provision) benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ (1,418)	$ (2,103)	$ (3,883)
State	523	(675)	(190)
Total current	(895)	(2,778)	(4,073)
Deferred:
Federal	3,722	777	5,011
State	118	80	(168)
Total deferred	3,840	857	4,843
Total provision for (benefit from) income taxes (1)	2,945	(1,921)	770
Tax benefit from investments in unconsolidated affiliates	$ 0	$ (770)	$ 0