Income Taxes - Components of income tax provision (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Taxes
Statutory federal income tax rate (as a percent)	34.00%	34.00%	34.00%	34.00%
Income tax at federal rate	$ (1,781)	$ (154)	$ (4,915)	$ 752
Increase (decrease) resulting from:
State income taxes, net of federal income tax	(224)	(3)	(580)	143
Expense not deductible for tax		36		196
Tax credit included in taxable income	(21)		171
Other permanent differences	35	21	107	126
Capital goods excise tax debit	62
Capital goods excise tax credit		(74)	(500)	(325)
Change in valuation allowance	89,410		89,410
Total income tax provision (benefit)	87,481	(174)	$ 83,693	892
Cumulative loss, number of years considered in DTA assessment			3 years
Unrecognized tax benefits	0		$ 0
Interest or penalties related to tax assessments recognized	$ 0	$ 0	$ 0	$ 0