Summary of Significant Accounting Policies - Adoption of ASC 606 (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable		$ 47,986	$ 35,690		$ 40,597
Accumulated deficit		(352,809)	(280,799)		(275,892)
Precision oncology testing	[1]	180,462	78,407	$ 42,088
Development services	[1]	33,913	$ 12,232	$ 7,754
Balances Without Adoption of ASC 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable		47,639
Accumulated deficit		(353,156)
Precision oncology testing		180,115
Development services		33,913
Topic 606 adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable		(347)			4,907
Accumulated deficit		(347)			$ 4,907
Topic 606 adoption | Effect of Change
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Precision oncology testing		(347)
Development services		$ 0

[1] Fiscal year 2018 and 2017 results do not reflect the impact of the adoption of the new revenue accounting standard in fiscal year 2019.