Condensed Consolidated Statements of Operations and Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Revenue	$ 18,309	$ 14,253	$ 37,604	$ 25,431
Related-party revenue from Roche	4,149	243	4,149	520
Total revenue	22,458	14,496	41,753	25,951
Costs and expenses:
Cost of revenue	8,950	6,619	17,866	11,910
Selling and marketing	12,542	7,170	22,363	12,860
General and administrative	23,769	5,825	32,611	11,525
Research and development	10,256	8,645	18,944	15,560
Total costs and expenses	55,517	28,259	91,784	51,855
Loss from operations	(33,059)	(13,763)	(50,031)	(25,904)
Other income (expense):
Interest income	9	2	16	7
Interest expense		(18)		(48)
Total other income (expense), net	9	(16)	16	(41)
Net loss	$ (33,050)	$ (13,779)	$ (50,015)	$ (25,945)
Net loss per common share, basic and diluted	$ (0.98)	$ (0.49)	$ (1.60)	$ (0.93)
Weighted-average common shares outstanding, basic and diluted	33,852,919	27,876,931	31,245,617	27,804,914
Comprehensive loss	$ (33,050)	$ (13,779)	$ (50,015)	$ (25,945)