Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue:
Total revenue	$ 57,006	$ 35,004	$ 109,846	$ 61,332
Costs and expenses:
Selling and marketing	17,141	17,115	34,621	33,551
General and administrative	19,771	17,648	40,466	32,925
Research and development	24,702	22,973	48,561	46,258
Total costs and expenses	89,090	79,318	178,351	152,333
Loss from operations	(32,084)	(44,314)	(68,505)	(91,001)
Interest (expense) income, net	(1,477)	56	(2,471)	146
Other income	182		182	144
Net loss	(33,379)	(44,258)	(70,794)	(90,711)
Other comprehensive (loss)/income:
Unrealized gain/(loss) on available-for-sale securities		12		(6)
Foreign currency translation adjustment	(23)	102	(309)	85
Total other comprehensive (loss)/income	(23)	114	(309)	79
Comprehensive loss	$ (33,402)	$ (44,144)	$ (71,103)	$ (90,632)
Net loss per common share, basic and diluted	$ (0.90)	$ (1.24)	$ (1.92)	$ (2.55)
Weighted-average common shares outstanding, basic and diluted	37,068,518	35,660,430	36,931,510	35,544,003
Molecular Information Services [Member]
Revenue:
Revenue	$ 38,702	$ 24,777	$ 70,478	$ 40,371
Costs and expenses:
Cost of molecular information services	22,676	19,537	43,955	36,654
Pharma Research and Development Services [Member]
Revenue:
Revenue	3,732	1,215	8,514	2,302
Roche [Member] | Molecular Information Services [Member]
Revenue:
Related-party revenue	12,005	5,520	26,820	11,024
Costs and expenses:
Cost of related-party molecular information services from Roche	4,800	2,045	10,748	2,945
Roche [Member] | Pharma Research and Development Services [Member]
Revenue:
Related-party revenue	$ 2,567	$ 3,492	$ 4,034	$ 7,635