Property and Equipment - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Nov. 30, 2017
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 1,498	$ 997	$ 988
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Costs capitalized	300
Richmond Build-to-Suit Lease [Member]
Property, Plant and Equipment [Line Items]
Costs capitalized		$ 3,900
Brisbane Build-to-Suit Lease [Member]
Property, Plant and Equipment [Line Items]
Costs capitalized	21,200
Brisbane Build-to-Suit Lease [Member] | Building [Member]
Property, Plant and Equipment [Line Items]
Costs capitalized	$ 20,900			$ 20,900