Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Total
Stockholders' Equity, Beginning Balance at Dec. 31, 2015	$ 25	$ 219,122	$ (251)	$ (49,822)	$ 169,074
Shares, Outstanding, Beginning Balance at Dec. 31, 2015	24,930,979
Vesting of restricted stock	$ 1	17			18
Vesting of restricted stock (in shares)	601,501
Exercises of vested stock options		514			514
Exercises of vested stock options (in shares)	65,432
Stock based compensation expense		6,310			6,310
Unrealized gain (loss) on available for-sale securities, net of tax			199		199
Net loss				(40,193)	(40,193)
Stockholders' Equity, Ending Balance at Dec. 31, 2016	$ 26	225,963	(52)	(90,015)	135,922
Shares, Outstanding, Ending Balance at Dec. 31, 2016	25,597,912
Vesting of restricted stock	$ 1	12			13
Vesting of restricted stock (in shares)	573,803
Exercises of vested stock options		1,363			1,363
Exercises of vested stock options (in shares)	158,677
Issuance of common stock under ESPP		563			563
Issuance of common stock under ESPP (in shares)	66,652
Issuance of common stock from public offering (net of underwriters discounts and issuance costs of $4,100)	$ 5	57,989			57,994
Issuance of common stock from public offering (net of underwriters discounts and issuance costs of $4,100) (in shares)	5,175,000
Stock based compensation expense		9,129			9,129
Unrealized gain (loss) on available for-sale securities, net of tax			(235)		(235)
Net loss				(70,698)	(70,698)
Stockholders' Equity, Ending Balance at Dec. 31, 2017	$ 32	295,019	(287)	(160,713)	134,051
Shares, Outstanding, Ending Balance at Dec. 31, 2017	31,572,044
Vesting of restricted stock		9			9
Vesting of restricted stock (in shares)	319,891
Exercises of vested stock options		3,891			$ 3,891
Exercises of vested stock options (in shares)	384,186				384,186
Issuance of common stock under ESPP		969			$ 969
Issuance of common stock under ESPP (in shares)	88,774
Stock based compensation expense		15,710			15,710
Unrealized gain (loss) on available for-sale securities, net of tax			34		34
Impact of adopting new accounting standards | ASU 2016-01			120	(120)
Impact of adopting new accounting standards | ASU 2014-09				(19,930)	(19,930)
Impact of adopting new accounting standards					20,050
Net loss				(88,288)	(88,288)
Stockholders' Equity, Ending Balance at Dec. 31, 2018	$ 32	$ 315,598	$ (133)	$ (269,051)	$ 46,446
Shares, Outstanding, Ending Balance at Dec. 31, 2018	32,364,895