Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue	$ 79,759	$ 60,221	$ 28,136
Related-party revenue from Roche	13,444	858	854
Total revenue	93,203	61,079	28,990
Costs and expenses:
Cost of revenue	36,695	27,434	11,659
Cost of Roche related-party revenue	2,736
Selling and marketing	49,030	28,997	12,326
General and administrative	50,614	27,302	21,865
Research and development	43,883	30,629	24,901
Total costs and expenses	182,958	114,362	70,751
Loss from operations	(89,755)	(53,283)	(41,761)
Other income (expense):
Interest income (expense), net	124	(42)	(235)
Other income (expense), net		1,103	(948)
Total other income (expense), net	124	1,061	(1,183)
Net loss	(89,631)	(52,222)	(42,944)
Other comprehensive loss:
Unrealized loss on available-for-sale securities	(178)
Total other comprehensive loss	(178)
Comprehensive loss	(89,809)	(52,222)	(42,944)
Reconciliation of net loss to net loss applicable to common stockholders:
Net loss	(89,631)	(52,222)	(42,944)
Accretion of redeemable convertible preferred stock			(139)
Net loss applicable to common stockholders	$ (89,631)	$ (52,222)	$ (43,083)
Net loss per common share applicable to common stockholders, basic and diluted	$ (2.73)	$ (1.87)	$ (4.64)
Weighted average common shares outstanding, basic and diluted	32,836,219	27,954,327	9,294,730