Stock-Based Compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 3,215	$ 1,180	$ 6,397	$ 2,457
Precision oncology testing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	126	79	296	142
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	1,428	214	2,638	418
Sales and marketing expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	646	259	1,472	633
General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,015	$ 628	$ 1,991	$ 1,264