Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Revenue	$ 73,388	$ 79,759	$ 60,221
Related-party revenue from Roche	43,477	13,444	858
Total revenue	116,865	93,203	61,079
Costs and expenses:
Cost of revenue	52,978	36,695	27,434
Cost of Roche related-party revenue	3,770	2,736
Selling and marketing	57,951	49,030	28,997
General and administrative	48,611	50,614	27,302
Research and development	67,371	43,883	30,629
Total costs and expenses	230,681	182,958	114,362
Loss from operations	(113,816)	(89,755)	(53,283)
Other income (expense):
Interest income (expense), net	624	124	(42)
Other income (expense), net			1,103
Total other income (expense), net	624	124	1,061
Net loss	(113,192)	(89,631)	(52,222)
Other comprehensive gain/(loss):
Unrealized gain/(loss) on available-for-sale securities	169	(178)
Foreign currency translation adjustment	(5)
Total other comprehensive gain/(loss)	164	(178)
Comprehensive loss	$ (113,028)	$ (89,809)	$ (52,222)
Net loss per common share, basic and diluted	$ (3.25)	$ (2.73)	$ (1.87)
Weighted average common shares outstanding, basic and diluted	34,794,347	32,836,219	27,954,327