Income Taxes - Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Federal statutory rate	21.00%	35.00%	35.00%
State income tax expense, net of federal benefits	(3.40%)	0.10%	4.90%
Nondeductible meals and entertainment	2.10%	0.60%	1.60%
Nondeductible employee fringe benefits	1.30%	0.00%	0.00%
Research and development tax credits	(48.70%)	(16.10%)	(10.80%)
Tax windfall benefits	(55.70%)	(36.50%)	(0.00%)
Change in tax rate due to tax reform	0.00%	27.80%	0.00%
Change in tax rate	(1.40%)	(0.60%)	(0.10%)
Other	0.80%	(1.00%)	(1.20%)
Effective rate	(84.00%)	9.30%	29.40%