Leases - Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Operating Lease Liabilities, Payments Due [Abstract]
2019 (remaining 9 months and 12 months, respectively)	$ 1,525
2020	1,788
2021	1,839
2022	1,894
2023	1,951
Thereafter	7,111
Total lease payments	16,108
Less imputed interest	(3,341)
Total operating lease liabilities	12,767
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2019 (remaining 9 months and 12 months, respectively)			$ 1,777
2020			1,788
2021			1,839
2022			1,894
2023			1,951
Thereafter			7,296
Total lease payment due			16,545
Assets and Liabilities, Lessee [Abstract]
Current portion of operating lease liabilities	1,412	$ 1,058	0
Operating lease liabilities, net of current portion	11,355	$ 11,776	$ 0
Total operating lease liabilities	$ 12,767