Income Taxes - Effective Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Federal statutory income tax rate	21.00%	35.00%
Federal and state tax credits	10.30%	(4.80%)
State income taxes, net of federal benefit	3.00%	3.10%
Change in valuation allowance	(32.50%)	14.50%
Other permanent items	(1.00%)	1.90%
Change in tax rate	(0.70%)	(40.70%)
Transaction costs	(0.00%)	(2.90%)
Net operating loss reduction	(0.00%)	(6.70%)
Other, net	(0.10%)	0.60%
Effective income tax rate	0.00%	0.00%