Revenue Recognition - Disaggregation (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total revenues	$ 66,965	$ 65,280	$ 63,069	$ 62,340	$ 52,050	$ 55,910	$ 52,283	$ 49,382	$ 257,654	$ 209,625	$ 212,512
Previously delivered tests, revenue recognized									10,200
Decrease to loss from operations									(114,628)	(135,341)	(101,050)
Adjustment
Disaggregation of Revenue [Line Items]
Decrease to loss from operations									$ 10,200
Net loss per share, basic and diluted (in dollars per share)									$ 0.18
United States
Disaggregation of Revenue [Line Items]
Total revenues									$ 225,931	185,533	188,492
Americas, excluding U.S.
Disaggregation of Revenue [Line Items]
Total revenues									3,472	3,028	2,562
Europe, Middle East, India, and Africa
Disaggregation of Revenue [Line Items]
Total revenues									20,866	13,998	14,256
Other
Disaggregation of Revenue [Line Items]
Total revenues									7,385	7,066	7,202
Insurance carriers
Disaggregation of Revenue [Line Items]
Total revenues									193,895	163,861	157,570
Laboratory partners
Disaggregation of Revenue [Line Items]
Total revenues									44,062	36,001	46,129
Patients
Disaggregation of Revenue [Line Items]
Total revenues									19,697	9,763	8,813
Panorama NIPT
Disaggregation of Revenue [Line Items]
Total revenues									140,932	128,896	140,582
HCS
Disaggregation of Revenue [Line Items]
Total revenues									87,171	63,467	56,417
Other genetic tests
Disaggregation of Revenue [Line Items]
Total revenues									12,263	11,414	12,407
Product
Disaggregation of Revenue [Line Items]
Total revenues									240,366	203,777	209,406
Constellation
Disaggregation of Revenue [Line Items]
Total revenues									4,844	4,229	3,106
Qiagen
Disaggregation of Revenue [Line Items]
Total revenues									5,794
Other product
Disaggregation of Revenue [Line Items]
Total revenues									6,650	1,619
Licensing and other
Disaggregation of Revenue [Line Items]
Total revenues									$ 17,288	$ 5,848	$ 3,106