Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Statement [Abstract]
Revenue	$ 20,953	$ 16,284	$ 58,557	$ 41,715
Related-party revenue from Roche	4,446	164	8,595	684
Total revenue	25,399	16,448	67,152	42,399
Costs and expenses:
Cost of revenue	9,068	7,502	26,934	19,412
Cost of Roche related-party revenue	1,302		1,302
Selling and marketing	14,267	7,893	36,630	20,753
General and administrative	9,199	6,801	41,810	18,326
Research and development	12,174	7,230	31,118	22,790
Total costs and expenses	46,010	29,426	137,794	81,281
Loss from operations	(20,611)	(12,978)	(70,642)	(38,882)
Other income (expense):
Interest income	15	8	31	14
Interest expense		(10)		(57)
Total other income (expense), net	15	(2)	31	(43)
Net loss	$ (20,596)	$ (12,980)	$ (70,611)	$ (38,925)
Net loss per common share, basic and diluted	$ (0.60)	$ (0.46)	$ (2.19)	$ (1.40)
Weighted-average common shares outstanding, basic and diluted	34,347,593	28,037,349	32,290,972	27,883,244
Comprehensive loss	$ (20,596)	$ (12,980)	$ (70,611)	$ (38,925)