Commitments and Contingencies - Additional Information (Detail) - Brisbane Build-to-Suit Lease [Member] $ in Millions	1 Months Ended	6 Months Ended
	Nov. 30, 2017 USD ($) ft² Option	Jun. 30, 2018 USD ($)
Commitments And Contingencies [Line Items]
Property leased | ft²	87,700
Lease expiration date		May 31, 2029
Operating lease expiration period	10 years
Number of lease term extension options | Option	2
Restricted cash	$ 3.5
Costs capitalized		$ 27.0
Building [Member]
Commitments And Contingencies [Line Items]
Costs capitalized	$ 20.9
Maximum [Member]
Commitments And Contingencies [Line Items]
Lease agreement, extendable lease term	10 years