Leases - Components of Lease Costs Included in Operating Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Leases [Abstract]
Operating lease cost	$ 4,116	$ 1,927	$ 10,030	$ 5,651
Variable lease cost	1,485	1,096	4,539	3,371
Total lease costs	$ 5,601	$ 3,023	$ 14,569	$ 9,022