Subsequent Events - Additional Information (Details) $ in Millions	6 Months Ended
	Jun. 30, 2019	Aug. 13, 2019 USD ($) ft²
Subsequent Event [Line Items]
Operating lease description	In August 2019, we entered into an operating lease to rent 100,000 square feet in a to-be-constructed building in Seattle, Washington. Shell construction is expected to be completed in 2020. The lease term commences on the date that the landlord delivers the premises to us for construction of certain tenant improvements. Rent obligations commence 10 months thereafter, and the lease term ends 142 months form the date rent commences, subject to our option to twice extend the lease for five years. The lease is cancellable under certain circumstances if the landlord fails to deliver the premises to us by May 1, 2021. We plan to occupy the new building in 2021, once interior construction is finished. The lease also requires us to pay additional amounts for operating and maintenance expenses.
Option to extend the lease term, description	our option to twice extend the lease for five years
Subsequent Event
Subsequent Event [Line Items]
Operating lease to rent in a to-be constructed building		100,000
Letter of credit | $		$ 2.1
Expand the size of the existing premises by area		8,400