Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Redeemable Convertible Preferred Stock Series A	Redeemable Convertible Preferred Stock Series B	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit	Total
Stockholders' Equity, Begining Balance at Dec. 31, 2013						$ (3,833)	$ (3,833)
Shares, Outstanding, Beginning Balance at Dec. 31, 2013			2,352
Issuance of common stock for services			$ 1	$ 251			252
Issuance of common stock for services			494,118
Initial issuance of Series A redeemable convertible preferred stock, including exchange of convertible notes payable and net of tranche rights and issuance costs	$ 3,878
Initial issuance of Series A redeemable convertible preferred stock, including exchange of convertible notes payable and net of tranche rights and issuance costs ( in shares)	6,500,000
Issuance of preferred stock, net of discount and issuance costs	$ 18,491
Reclassification of tranche rights upon issuance of Series A redeemable convertible preferred stock	(1,756)
Net loss						(16,317)	(16,317)
Vesting of restricted common stock				9			9
Vesting of restricted common stock (in shares)			318,364
Stock-based compensation expense				425			425
Accretion of redeemable convertible preferred stock to redemption value (Preferred Stock)	1,366
Accretion of redeemable convertible preferred stock to redemption value				685		681	1,366
Stockholders' Equity, Ending Balance at Dec. 31, 2014	$ 21,979		$ 1			(20,831)	(20,830)
Shares, Outstanding, Ending Balance at Dec. 31, 2014	25,000,000		814,834
Issuance of preferred stock, net of discount and issuance costs (in shares)	18,500,000
Issuance of common stock			$ 6	72,948			72,954
Issuance of common stock (in shares)			5,750,000
Issuance of preferred stock, net of discount and issuance costs	$ 19,999	$ 84,780
Reclassification of tranche rights upon issuance of Series A redeemable convertible preferred stock	16,055
Conversion of redeemable convertible preferred stock to common stock	$ (60,182)	$ (90,005)	$ 18	144,675		5,494	150,187
Conversion of redeemable convertible preferred stock to common stock (common stock shares)			17,647,054
Conversion of redeemable convertible preferred stock to common stock (preferred stock shares)	(45,000,000)	(30,000,001)
Net loss						(29,672)	(29,672)
Vesting of restricted common stock				22			22
Vesting of restricted common stock (in shares)			717,747
Stock-based compensation expense				4,027			4,027
Unrealized loss on available for-sale securities					$ (251)		(251)
Accretion of redeemable convertible preferred stock to redemption value (Preferred Stock)	$ 2,149	$ 5,225
Accretion of redeemable convertible preferred stock to redemption value				2,560		4,813	7,373
Exercises of vested stock options				10			10
Exercises of vested stock options (in shares)			1,344
Stockholders' Equity, Ending Balance at Dec. 31, 2015			$ 25	219,122	(251)	(49,822)	169,074
Shares, Outstanding, Ending Balance at Dec. 31, 2015			24,930,979
Issuance of preferred stock, net of discount and issuance costs (in shares)	20,000,000	30,000,001
Net loss						(40,193)	(40,193)
Vesting of restricted common stock			$ 1	17			18
Vesting of restricted common stock (in shares)			601,501
Stock-based compensation expense				6,310			6,310
Unrealized loss on available for-sale securities					199		199
Exercises of vested stock options				514			514
Exercises of vested stock options (in shares)			65,432
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