Stock-Based Compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 5,484	$ 1,831	$ 11,882	$ 4,288
Precision oncology testing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	266	112	562	254
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	2,066	617	4,704	1,035
Sales and marketing expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	1,458	428	2,930	1,061
General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,694	$ 674	$ 3,686	$ 1,938