Stock-Based Compensation - Stock Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,831	$ 808	$ 4,288	$ 2,098
Precision oncology testing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	112	(25)	254	104
Research and development expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	617	17	1,035	307
Sales and marketing expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	428	(526)	1,061	14
General and administrative expense
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 674	$ 1,342	$ 1,938	$ 1,673