Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2013	$ 131,711	$ 3	$ 221,471		$ (89,763)
Beginning Balance, shares at Dec. 31, 2013		27,630,781
Exercise of stock options	637		637
Exercise of stock options, shares		212,822
Vesting of restricted stock	54		54
Vesting of restricted stock, shares		380,355
Stock-based compensation expense	5,989		5,989
Net loss	(52,222)				(52,222)
Ending Balance at Dec. 31, 2014	86,169	$ 3	228,151		(141,985)
Ending Balance, shares at Dec. 31, 2014		28,223,958
Exercise of stock options	4,739		4,739
Exercise of stock options, shares		1,070,457
Vesting of restricted stock	27		27
Vesting of restricted stock, shares		219,430
Issuance of common stock from Roche transaction, net of issuance costs	245,387		245,387
Issuance of common stock from Roche transaction, net of issuance costs, Shares		5,000,000
Stock-based compensation expense	11,176		11,176
Other comprehensive loss	(178)			$ (178)
Net loss	(89,631)				(89,631)
Ending Balance at Dec. 31, 2015	257,689	$ 3	489,480	(178)	(231,616)
Ending Balance, shares at Dec. 31, 2015		34,513,845
Exercise of stock options	$ 652		652
Exercise of stock options, shares	167,853	167,853
Vesting of restricted stock	$ 9	$ 1	8
Vesting of restricted stock, shares		599,303
Stock-based compensation expense	19,524		19,524
Other comprehensive loss	164			164
Net loss	(113,192)				(113,192)
Ending Balance at Dec. 31, 2016	$ 164,846	$ 4	$ 509,664	$ (14)	$ (344,808)
Ending Balance, shares at Dec. 31, 2016		35,281,001