Revenue Recognition - Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 65,280	$ 55,910	$ 190,689	$ 157,575
United States
Disaggregation of Revenue [Line Items]
Total revenues	58,651	49,896	165,646	139,728
Americas, excluding U.S.
Disaggregation of Revenue [Line Items]
Total revenues	932	773	2,629	2,258
Europe, Middle East, India, Africa
Disaggregation of Revenue [Line Items]
Total revenues	3,711	3,443	16,789	10,279
Other
Disaggregation of Revenue [Line Items]
Total revenues	1,986	1,798	5,625	5,310
Insurance carriers
Disaggregation of Revenue [Line Items]
Total revenues	50,631	44,410	143,094	124,272
Laboratory partners
Disaggregation of Revenue [Line Items]
Total revenues	9,162	9,286	34,182	26,558
Patients
Disaggregation of Revenue [Line Items]
Total revenues	5,487	2,214	13,413	6,745
Panorama NIPT
Disaggregation of Revenue [Line Items]
Total revenues	35,999	33,889	104,981	97,975
HCS
Disaggregation of Revenue [Line Items]
Total revenues	23,565	17,900	63,248	47,325
Other genetic tests
Disaggregation of Revenue [Line Items]
Total revenues	3,098	2,723	9,055	8,535
Product
Disaggregation of Revenue [Line Items]
Total revenues	62,662	54,512	177,284	153,835
Constellation
Disaggregation of Revenue [Line Items]
Total revenues	1,054	1,058	3,652	3,091
Other, licensing and other
Disaggregation of Revenue [Line Items]
Total revenues	1,564	340	9,753	649
Licensing and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 2,618	$ 1,398	$ 13,405	$ 3,740