Income Taxes - Reconciliation (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate
State taxes, net of federal benefit (as a percent)	6.90%	4.60%
Foreign rate differential (as a percent)	(3.00%)	(3.40%)
Disregarded entity (as a percent)	15.90%	12.00%
Research and development tax credits (as a percent)	1.40%	1.40%
Permanent difference (as a percent)	0.10%	(0.50%)
Valuation allowances (as a percent)	(42.40%)	(35.10%)
Foreign withholding tax (as a percent)	(1.50%)	(1.40%)
Effective income tax rate (as a percent)	(1.60%)	(1.40%)
U.K.
Reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate
Income tax benefit computed at statutory tax rate (as a percent)	21.00%	21.00%