Leases - Components of Lease Costs Included in Operating Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Leases [Abstract]
Operating lease cost	$ 2,957	$ 1,886	$ 5,914	$ 3,724
Variable lease cost	1,781	1,182	3,054	2,275
Total lease costs	$ 4,738	$ 3,068	$ 8,968	$ 5,999