Income Taxes - Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
U.S. federal statutory income tax rate	(21.00%)	(21.00%)	(34.00%)
State taxes, net of federal tax benefit	(3.83%)	(3.07%)	(2.62%)
Permanent and other differences	(0.25%)	(0.26%)	(2.31%)
Change in tax rates	0.16%	(0.41%)	(1.02%)
Tax rate differential	3.28%	4.92%	8.99%
Tax cuts and jobs act	0	0	0.3846
Unrecognized tax benefits	0.79%	0.81%	1.20%
Nondeductible equity and other compensation	1.12%	(0.17%)	(4.31%)
Credit for increased research activities	(2.80%)	(3.12%)	(4.42%)
Change in Valuation allowance	22.40%	22.54%	0.81%
Effective tax rate	(0.13%)	0.24%	0.78%