Commitments and Contingencies - Additional Information (Details)	1 Months Ended		12 Months Ended
	Oct. 31, 2018 USD ($) ft²	Sep. 30, 2018 USD ($) ft²	Dec. 31, 2018 USD ($) ft² Facility	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Commitments And Contingencies Disclosure [Line Items]
Purchase commitment cancellation notice period			30 days
Aggregate future minimum rental payments due			$ 96,308,000
Rent expense net			2,100,000	$ 1,400,000	$ 1,300,000
Contingent liability for accrual			$ 0	$ 0
Facilities
Commitments And Contingencies Disclosure [Line Items]
Area of leased property | ft²	22,100	129,800	48,400
Facilities available for operating lease | Facility			2
Lease expiration date			Jan. 31, 2020
Lease period	15 months	10 years
Lease commencement period	2019-02
Aggregate future minimum rental payments due	$ 1,100,000	$ 93,200,000
Rent commencement date		2020-01
Additional period of extension in lease contract		10 years
Standby letter of credit		$ 1,900,000