Revenue Recognition - Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 63,069	$ 52,283	$ 125,409	$ 101,665
United States
Disaggregation of Revenue [Line Items]
Total revenues	56,631	46,007	106,995	89,832
Americas, excluding U.S.
Disaggregation of Revenue [Line Items]
Total revenues	847	785	1,697	1,485
Europe, Middle East, India, Africa
Disaggregation of Revenue [Line Items]
Total revenues	3,756	3,620	13,078	6,836
Other
Disaggregation of Revenue [Line Items]
Total revenues	1,835	1,871	3,639	3,512
Insurance carriers
Disaggregation of Revenue [Line Items]
Total revenues	48,321	41,022	92,463	79,862
Laboratory partners
Disaggregation of Revenue [Line Items]
Total revenues	10,132	9,179	25,020	17,272
Patients
Disaggregation of Revenue [Line Items]
Total revenues	4,616	2,082	7,926	4,531
Panorama NIPT
Disaggregation of Revenue [Line Items]
Total revenues	35,715	31,527	68,982	64,086
HCS
Disaggregation of Revenue [Line Items]
Total revenues	21,421	16,472	39,683	29,425
Other genetic tests
Disaggregation of Revenue [Line Items]
Total revenues	3,217	2,930	5,957	5,812
Product
Disaggregation of Revenue [Line Items]
Total revenues	60,353	50,929	114,622	99,323
Constellation
Disaggregation of Revenue [Line Items]
Total revenues	1,293	1,045	2,598	2,033
Other, licensing and other
Disaggregation of Revenue [Line Items]
Total revenues	1,423	309	8,189	309
Licensing and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 2,716	$ 1,354	$ 10,787	$ 2,342