Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders Equity - USD ($) $ in Thousands	Total	IPO	Follow-on Offering	Conversion of Series A into Common Stock During IPO	Conversion of Series A-1 into Common Stock During IPO	Conversion Of Series B Into Common Stock During I P O	Series A Redeemable Convertible Preferred Stock	Series A Redeemable Convertible Preferred Stock Conversion of Series A into Common Stock During IPO	Series A-1 Redeemable Convertible Preferred Stock	Series A-1 Redeemable Convertible Preferred Stock Conversion of Series A-1 into Common Stock During IPO	Series B Redeemable Convertible Preferred Stock	Series B Redeemable Convertible Preferred Stock Conversion Of Series B Into Common Stock During I P O	Common Stock	Common Stock IPO	Common Stock Follow-on Offering	Common Stock Conversion of Series A into Common Stock During IPO	Common Stock Conversion of Series A-1 into Common Stock During IPO	Common Stock Conversion Of Series B Into Common Stock During I P O	Additional Paid-In Capital	Additional Paid-In Capital IPO	Additional Paid-In Capital Follow-on Offering	Additional Paid-In Capital Conversion of Series A into Common Stock During IPO	Additional Paid-In Capital Conversion of Series A-1 into Common Stock During IPO	Additional Paid-In Capital Conversion Of Series B Into Common Stock During I P O	Accumulated Other Comprehensive Income/ (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2013	$ (17,247)																									$ (17,247)
Beginning balance, shares at Dec. 31, 2013													3,178,081
Beginning balance, redeemable convertible preferred stock at Dec. 31, 2013							$ 19,388
Beginning balance, redeemable convertible preferred stock, shares at Dec. 31, 2013							19,250,000
Issuance of redeemable convertible preferred stock, net of issuance costs, value							$ 19,282		$ 9,896
Issuance of redeemable convertible preferred stock, net of issuance costs, shares							19,000,000		6,666,667
Issuance of common stock for stock option exercises, value	4																		$ 4
Issuance of common stock for stock option exercises, shares													480,723
Repurchase of early exercised stock options, value	(8)																		(8)
Repurchase of early exercised stock options, shares													(24,370)
Vesting of early exercised stock options and restricted stock	104																		104
Share-based compensation	92																		92
Dividends on redeemable convertible preferred stock							$ 2,537		$ 327
Redeemable convertible preferred stock dividends	(2,864)																		(192)							(2,672)
Accretion of redeemable convertible preferred stock to redemption value							152		6
Accretion of convertible preferred stock value	(158)																									(158)
Net loss	(16,829)																									(16,829)
Ending balance at Dec. 31, 2014	$ (36,906)																									(36,906)
Ending balance, shares at Dec. 31, 2014													3,634,434
Ending balance, redeemable convertible preferred stock at Dec. 31, 2014							$ 41,359		$ 10,229
Ending balance, redeemable convertible preferred stock, shares at Dec. 31, 2014							38,250,000		6,666,667
Issuance of common stock during offering, net of issuance costs, value		$ 55,627												$ 1						$ 55,626
Issuance of common stock during offering, net of issuance costs, shares														6,253,125
Issuance of redeemable convertible preferred stock, net of issuance costs, value											$ 45,837
Issuance of redeemable convertible preferred stock, net of issuance costs, shares											17,068,646
Issuance of common stock for stock option exercises, shares	352,978												352,978
Repurchase of early exercised stock options, value	$ (19)																		(19)
Repurchase of early exercised stock options, shares													(54,128)
Vesting of early exercised stock options and restricted stock	177																		177
Share-based compensation	516																		516
Dividends on redeemable convertible preferred stock							$ 2,541		$ 663		$ 1,947
Redeemable convertible preferred stock dividends	(5,151)																		(416)							(4,735)
Accretion of redeemable convertible preferred stock to redemption value							$ 73		$ 12		$ 12								500
Accretion of convertible preferred stock value	(98)																									(98)
Conversion of redeemable convertible preferred stock into common stock, value, shares								(38,250,000)		(6,666,667)		(17,068,646)				10,408,162	1,814,059	4,644,526
Conversion of redeemable convertible preferred stock into common stock, value				$ 43,973	$ 10,904	$ 47,796		$ (43,973)		$ (10,904)		$ (47,796)				$ 1		$ 1				$ 43,972	$ 10,904	$ 47,795
Net loss	(22,946)																									(22,946)
Ending balance at Dec. 31, 2015	93,873												$ 3						158,555							(64,685)
Ending balance, shares at Dec. 31, 2015													27,053,156
Issuance of common stock during offering, net of issuance costs, value			$ 61,110																		$ 61,110
Issuance of common stock during offering, net of issuance costs, shares															4,370,000
Issuance of common stock for stock option exercises, value	$ 13																		13
Issuance of common stock for stock option exercises, shares	18,913												18,913
Issuance of common stock for employee stock purchase plan, value	$ 493																		493
Issuance of common stock for employee stock purchase plan, shares													52,913
Repurchase of early exercised stock options, value	(48)																		(48)
Repurchase of early exercised stock options, shares													(65,984)
Vesting of early exercised stock options and restricted stock	272																		272
Share-based compensation	2,813																		2,813
Unrealized gains/(losses), net of tax benefits	8																								$ 8
Net loss	(13,152)																									(13,152)
Ending balance at Dec. 31, 2016	$ 145,382												$ 3						$ 223,208						$ 8	$ (77,837)
Ending balance, shares at Dec. 31, 2016													31,428,998