Property and Equipment - Additional Information (Detail) $ in Thousands	1 Months Ended		9 Months Ended
	Oct. 31, 2017 USD ($)	Feb. 28, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($) ft²
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment			$ 44,168	$ 24,039
Danvers
Property Plant And Equipment [Line Items]
Reclassification of leasehold improvement to building and building improvements	$ 32,600
Danvers | Land and Building
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment	16,500
Danvers | Land
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment	3,000
Danvers | Building and Building Improvements
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment	$ 13,000
Europe | Lease Agreements
Property Plant And Equipment [Line Items]
Office space under lease | ft²				33,000
Europe | Land and Building
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment		$ 12,600
Europe | Land
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment		4,000
Europe | Building and Building Improvements
Property Plant And Equipment [Line Items]
Acquisition cost for property and equipment		$ 8,600