Income Taxes - Provision for income taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal									$ (719)	$ 215	$ 904
State and local									1,119	(963)	(1,628)
Foreign									1	0	0
Total current income tax provision (benefit)									401	(748)	(724)
Deferred federal									16,513	(16,602)	31,029
Deferred state and local									1,188	(2,704)	2,961
Deferred Foreign Income Tax Expense (Benefit)									(4)	0	0
Total deferred income tax provision (benefit)									17,697	(19,306)	33,990
Provision (benefit) for income taxes	$ 9,938	$ 7,208	$ 2,983	$ (2,031)	$ (507)	$ (18,776)	$ 4,884	$ (5,655)	$ 18,098	$ (20,054)	$ 33,266