Leases - Reconciliation of Undiscounted Future Minimum Lease Payments Remaining Under Leases that Have Not Yet Commenced and Other Operating Leases (Detail) $ in Thousands	Jun. 30, 2019 USD ($)
Undiscounted future minimum lease payments:
2019 (remainder of year)	$ 1,298
2020	3,273
2021	4,720
2022	6,045
2023	6,855
Thereafter	83,650
Total undiscounted future minimum lease payments	105,841
Current portion of operating lease liabilities	(2,276)
Operating lease liabilities, non-current	4,654
Leases Not Yet Commenced [Member]
Undiscounted future minimum lease payments:
2019 (remainder of year)	98
2020	460
2021	2,308
2022	5,422
2023	6,376
Thereafter	83,650
Total undiscounted future minimum lease payments	98,314
Other Operating leases [Member]
Undiscounted future minimum lease payments:
2019 (remainder of year)	1,200
2020	2,813
2021	2,412
2022	623
2023	479
Total undiscounted future minimum lease payments	7,527
Amount representing imputed interest	(597)
Total operating lease liabilities	6,930
Current portion of operating lease liabilities	(2,276)
Operating lease liabilities, non-current	$ 4,654