Summary of Significant Accounting Policies - Adoption of ACS 606 (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable	$ 28,989		$ 40,597	$ 35,690
Accumulated deficit	(303,209)		(275,892)	$ (280,799)
Precision oncology testing	28,837	$ 14,191
Development services	7,818	$ 2,501
Topic 606 adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable			4,907
Accumulated deficit			$ 4,907
Effect of Change | Topic 606 adoption
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable	994
Accumulated deficit	994
Precision oncology testing	994
Development services	0
Balances Without Adoption of ASC606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts receivable	29,983
Accumulated deficit	(302,215)
Precision oncology testing	29,831
Development services	$ 7,818