Income Taxes (Income Tax Benefit Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax benefit at statutory U.S. federal income tax rate	$ (18,958)	$ (4,889)	$ (3,040)
State income tax — net of federal income tax benefit	(2,488)	(1,118)	(676)
Impact of Tax Cuts and Job Act	(15,720)
Charitable contributions			(469)
Adjustment to deferred tax depreciation			1,135
Change in deferred state tax rate		(1,082)
Research and development tax credits	(170)	(253)	(286)
Purchase price adjustment			393
Changes in unrecognized tax benefits	10	10	(186)
Changes in valuation allowance	1,152	1,031	270
Other	564	510	362
Income tax provision (benefit)	$ (35,610)	$ (5,791)	$ (2,497)