Revenue Recognition (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 31, 2019	Feb. 28, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Revenue recognized					$ 2,756	$ 1,895
Deferred revenue, Long-term			$ 23,128		23,128		$ 23,808
Other assets			12,156		12,156		12,476
Deferred revenue			74,355		74,355		79,824
Deferred revenue, current portion			51,227		51,227		56,016
Total revenues			98,143	$ 77,909	278,627	219,088
Deferred revenue, long-term portion			23,128		23,128		23,808
Revenue recognized during the period that was included in deferred revenues at the beginning of the period					5,290
Product
Revenue recognized			1,100	600	2,700	1,900
Cost of revenues			46,873	40,138	131,124	123,125
Total revenues			93,286	66,936	$ 260,746	195,399
Product | Minimum
Billing collection period (in months)					9 months
Product | Maximum
Billing collection period (in months)					12 months
Licensing and other
Cost of revenues			4,948	3,742	$ 12,614	7,883
Total revenues			4,857	10,973	17,881	23,689
Genetic testing services
Revenue recognized during the period that was included in deferred revenues at the beginning of the period					$ 400
Qiagen
Proceeds from license agreement								$ 5,000
Agreement term					10 years
Revenue, remaining performance obligation								40,000
Qiagen | Volume, regulatory and commercial milestones
Revenue, remaining performance obligation								$ 10,000
Qiagen | Prepaid royalty
Revenue recognized			0
Laboratory distribution partners | Product | Minimum
Billing collection period (in months)					2 months
Laboratory distribution partners | Product | Maximum
Billing collection period (in months)					3 months
BGI Genomics
Proceeds from license agreement		$ 50,000		35,600
Receivable				2,500		2,500
Agreement term		10 years
Deferred revenue, current portion			4,700		$ 4,700
BGI Genomics | Sequencing services
Other assets				6,000		6,000
BGI Genomics | Sequencing products
Other assets				4,000		4,000
BGI Genomics | Sequencing products and services
Other assets			10,000	$ 10,000	10,000	$ 10,000
Foundation Medicine ("FMI")
Proceeds from license agreement					0		16,300
Agreement term	5 years
Automatic renewals, successive period thereafter	1 year
Deferred revenue, current portion			$ 7,000		7,000
Foundation Medicine ("FMI") | Upfront licensing fees and prepaid revenues
Initial transaction price	$ 13,300
Foundation Medicine ("FMI") | Developmental, regulatory, and commercial milestones
Initial transaction price	$ 32,000
Foundation Medicine ("FMI") | Developmental performance milestones
Proceeds from license agreement							3,000
Foundation Medicine ("FMI") | Licensing fees and prepaid revenue
Proceeds from license agreement							$ 13,300
BGI and FMI | Genetic testing services
Revenue recognized during the period that was included in deferred revenues at the beginning of the period					$ 4,900