Commitments and Contingencies - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($) ft²	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Operating Leased Assets [Line Items]
Rent expense under operating leases	$ 3.1	$ 3.4	$ 2.9
Inventory purchase commitment, amount	$ 9.6
Seattle
Operating Leased Assets [Line Items]
Operating lease agreements, expiration year	2023
Office space leased | ft²	39,000
Minimum
Operating Leased Assets [Line Items]
Operating lease agreements, expiration year	2019
Maximum
Operating Leased Assets [Line Items]
Operating lease agreements, expiration year	2026