Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Total revenue	$ 152,903	$ 116,865	$ 93,203
Costs and expenses:
Selling and marketing	66,727	57,951	49,030
General and administrative	70,340	48,611	50,614
Research and development	91,509	67,371	43,883
Total costs and expenses	313,846	230,681	182,958
Loss from operations	(160,943)	(113,816)	(89,755)
Interest (expense) income, net	(727)	624	124
Other income	204
Net loss	(161,466)	(113,192)	(89,631)
Other comprehensive income (loss):
Unrealized gain/(loss) on available-for-sale securities	9	169	(178)
Foreign currency translation adjustment	114	(5)
Total other comprehensive income (loss)	123	164	(178)
Comprehensive loss	$ (161,343)	$ (113,028)	$ (89,809)
Net loss per common share, basic and diluted	$ (4.50)	$ (3.25)	$ (2.73)
Weighted-average common shares outstanding, basic and diluted	35,877,678	34,794,347	32,836,219
Molecular Information Services [Member]
Revenue:
Revenue	$ 91,695	$ 60,255	$ 71,766
Costs and expenses:
Cost of molecular information services	76,256	52,978	36,695
Pharma Research and Development Services [Member]
Revenue:
Revenue	10,922	13,133	7,993
Roche [Member] | Molecular Information Services [Member]
Revenue:
Related-party revenue	25,458	21,493	13,132
Costs and expenses:
Cost of related-party molecular information services from Roche	9,014	3,770	2,736
Roche [Member] | Pharma Research and Development Services [Member]
Revenue:
Related-party revenue	$ 24,828	$ 21,984	$ 312