Leases - Summary of Minimum Lease Payments for Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
2019 (9 months remaining)	$ 5,777
2020	8,399
2021	8,624
2022	8,888
2023	9,160
Thereafter	59,462
Total operating lease payments	100,310
Less accreted interest	(29,896)
Total operating lease liabilities	70,414
Less current operating lease liabilities	(3,267)
Noncurrent operating lease liabilities	$ 67,147	$ 0