Leases - Additional Information (Detail) $ in Thousands	3 Months Ended
	Sep. 30, 2019 USD ($) Lease	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Operating lease right of use assets	$ 24,845
Operating lease liabilities	29,100
Deferred Rent Credit			$ 4,000
Operating leases			$ 18,034
Increase in right of use asset	6,200
Increase in operating lease liabilities	$ 6,200
Waltham And Massachusetts [Member]
Number Of Operating leases | Lease	0.02
Accounting Standards Update 2016-02 [Member]
Operating lease right of use assets		$ 17,000
Operating lease liabilities		$ 21,000