Deferred Revenue - Additional Information (Details) - USD ($) $ in Thousands		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Disaggregation Of Revenue [Line Items]
Current deferred revenue	$ 60,994	$ 60,994	$ 12,695
Deferred revenue, less current portion	219,332	219,332	704
Revenue recognized	8,500	(50,624)
Development Revenue
Disaggregation Of Revenue [Line Items]
Current deferred revenue	48,512	48,512	1,457
Deferred revenue, less current portion	217,873	217,873	188
Development Revenue | Genentech, Inc.
Disaggregation Of Revenue [Line Items]
Current deferred revenue	48,100	48,100
Deferred revenue, less current portion	216,800	216,800
Sequencing Revenue
Disaggregation Of Revenue [Line Items]
Current deferred revenue	12,482	12,482	11,238
Deferred revenue, less current portion	$ 1,459	1,459	$ 516
Revenue recognized		$ 1,900