Revenue Recognition - Disaggregation (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Total revenues	$ 62,340	$ 49,382	$ 49,382
United States
Disaggregation of Revenue [Line Items]
Total revenues	50,364	43,825
Americas, excluding U.S.
Disaggregation of Revenue [Line Items]
Total revenues	850	700
Europe, Middle East, India, Africa
Disaggregation of Revenue [Line Items]
Total revenues	9,322	3,216
Other
Disaggregation of Revenue [Line Items]
Total revenues	1,804	1,641
Insurance carriers
Disaggregation of Revenue [Line Items]
Total revenues	44,142	38,840
Laboratory partners
Disaggregation of Revenue [Line Items]
Total revenues	14,888	8,093
Patients
Disaggregation of Revenue [Line Items]
Total revenues	3,310	2,449
Panorama NIPT
Disaggregation of Revenue [Line Items]
Total revenues	33,267		32,559
HCS
Disaggregation of Revenue [Line Items]
Total revenues	18,262		12,953
Other genetic tests
Disaggregation of Revenue [Line Items]
Total revenues	2,740		2,882
Product
Disaggregation of Revenue [Line Items]
Total revenues	54,269	48,394	48,394
Constellation
Disaggregation of Revenue [Line Items]
Total revenues	1,305		988
Other, licensing and other
Disaggregation of Revenue [Line Items]
Total revenues	6,766
Licensing and other
Disaggregation of Revenue [Line Items]
Total revenues	$ 8,071	$ 988	$ 988