Commitments and Contingencies - Additional Information (Detail)	1 Months Ended			12 Months Ended
	Jun. 30, 2018	Apr. 30, 2018 ft²	Jun. 30, 2014 ft²	Dec. 31, 2018 USD ($) ft²	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Operating Leased Assets [Line Items]
Rent expense | $				$ 1,400,000	$ 1,300,000	$ 1,300,000
Purchase commitments | $				$ 0	$ 0
Lease Agreement | Oakwood Village, Ohio
Operating Leased Assets [Line Items]
Area of land | ft²				19,800
Lease agreement, expiration date				Oct. 31, 2019
Lease agreement, option to extend expiration date				Oct. 31, 2021
Lease Agreement | Mountain View, California
Operating Leased Assets [Line Items]
Area of land | ft²		24,600	25,500
Lease agreement, expiration date	Jul. 31, 2025		Nov. 30, 2019
Lease agreement, term of contract		7 years
Lease commencement date		2018-12
Lease Agreement | Mountain View, California | Maximum
Operating Leased Assets [Line Items]
Lease agreement, renewal term		5 years