Income Taxes - Effective Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income before income tax expense (benefit)	$ 11,559	$ 22,971	$ 26,298
Income taxes computed at the Federal statutory rate	4,046	8,040	9,204
State income taxes, net of Federal benefit	472	867	1,021
Impact of 2017 Tax Act	24,235	0	0
Research and development and other tax credits	(1,775)	0	0
Change in valuation allowance	0	0	(64,159)
Other	(113)	85	(14)
Income tax expense (benefit)	$ 26,865	$ 8,992	$ (53,948)
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income taxes computed at the Federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of Federal benefit	4.10%	3.80%	3.90%
Impact of 2017 Tax Act	209.70%	0.00%	0.00%
Research and development and other tax credits	(15.40%)	(0.00%)	(0.00%)
Change in valuation allowance	0.00%	0.00%	(244.00%)
Other	(1.00%)	0.40%	(0.10%)
Income tax expense (benefit)	232.40%	39.10%	(205.10%)