Commitments and Contingencies - Narrative (Details) $ in Thousands		12 Months Ended
	May 02, 2018 USD ($) ft²	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Oct. 31, 2018 ft²
Loss Contingencies [Line Items]
Right of use asset		$ 33,923
Operating lease liability, current		3,665
Non-current operating lease liability		$ 68,865
Discount rate (as a percentage)		9.00%
Operating lease costs		$ 10,200
Rent expense			$ 6,000	$ 2,200
Weighted average remaining lease term		9 years 3 months 18 days
Weighted-average discount rate (as a percentage)		9.00%
Cash paid for lease liabilities		$ 5,400
Sublease income		2,600
Sublease income			0	0
Contractual obligation		1,100	1,200
Headquarters Lease
Loss Contingencies [Line Items]
Area under lease | ft²	148,020
Lease period	10 years
Lease renewal option term	10 years
New Premises Sublease Agreement
Loss Contingencies [Line Items]
Rentable square feet | ft²					36,835
Sublease term					5 years
Landlord Funded Tenant Improvements | Headquarters Lease
Loss Contingencies [Line Items]
Tenant improvement allowance repayable in rent	$ 4,400
DMSA
Loss Contingencies [Line Items]
Purchase order executed		21,200	24,700
Costs incurred		12,700	3,900	0
Payments for development and manufacturing services		12,500	3,400	$ 0
Non-Cancellable Purchase Commitments
Loss Contingencies [Line Items]
Non-refundable purchase commitments		$ 11,200	$ 14,000
Minimum | Headquarters Lease
Loss Contingencies [Line Items]
Lease renewal notice period	9 months
Maximum | Headquarters Lease
Loss Contingencies [Line Items]
Lease renewal notice period	12 months
Maximum | Landlord Funded Tenant Improvements | Headquarters Lease
Loss Contingencies [Line Items]
Tenant improvements	$ 25,900