Income Taxes - Income Tax Expense (Benefit) Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Amount computed using the statutory rate	$ (1,973)	$ (2,655)	$ (31,623)
Impact of rate change on deferred tax	0	64,915	0
State & local taxes	(1,731)	(368)	(2,000)
Percentage depletion carryforward	(256)	(66)	(163)
Non-deductible stock option expense	98	305	77
Share-based compensation	0	64	707
Restructuring costs	1,528	0	0
Other	93	(21)	1,415
Change in valuation allowance	2,393	(63,123)	32,130
Income tax expense (benefit)	$ 152	$ (949)	$ 543