Leases - Future Minimum Annual Obligations under Finance and Operating Lease Commitments (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating Leases, Remaining in 2019	$ 2,363
Operating Leases, 2020	3,231
Operating Leases, 2021	3,247
Operating Leases, 2022	3,333
Operating Leases, 2023	3,433
Operating Leases, 2024	3,536
Operating Leases, Thereafter	10,284
Operating Leases, Total minimum lease payments	29,427
Operating Leases, Imputed interest	(9,957)
Operating Leases, Total	19,470
Operating Leases, Less: leases, current	(3,171)
Operating Leases, Leases, net of current	16,299
Finance Leases, Remaining in 2019	55
Finance Leases, 2020	74
Finance Leases, 2021	18
Finance Leases, 2022	0
Finance Leases, 2023	0
Finance Leases, 2024	0
Finance Leases, Thereafter	0
Finance Leases, Total minimum lease payments	147
Finance Leases, Imputed interest	(13)
Finance Leases, Total	134
Finance Leases, Less: leases, current	(74)
Finance Leases, Leases, net of current	60
Remaining in 2019	2,418
2020	3,305
2021	3,265
2022	3,333
2023	3,433
2024	3,536
Thereafter	10,284
Total minimum lease payments	29,574
Imputed interest	(9,970)
Total	19,604
Less: leases, current	(3,245)	$ 0
Leases, net of current	$ 16,359	$ 0