Stockholders' Equity - Additional Information (Details)				1 Months Ended	2 Months Ended	12 Months Ended
	Feb. 21, 2017 shares	Mar. 06, 2014	Dec. 23, 2013 USD ($) $ / shares shares	May 31, 2016 USD ($)	Mar. 12, 2018 USD ($) shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 shares	Mar. 25, 2014 shares	Feb. 28, 2014 shares
Class of Stock [Line Items]
Common stock, shares authorized						175,000,000	175,000,000
Common stock, par value | $ / shares						$ 0.00001	$ 0.00001
Common stock, shares issued						47,612,619	38,615,709
Common stock, shares outstanding						47,612,619	38,615,709
Preferred stock, shares authorized						25,000,000	25,000,000
Preferred stock, par value | $ / shares						$ 0.00001	$ 0.00001
Preferred stock, shares issued						0	0
Preferred stock, shares outstanding						0	0
Stock split, conversion ratio		1.75
Convertible redeemable preferred stock converted into common stock									0	12,115,183
Proceeds from the issuance of common stock, net of issuance costs | $						$ 114,580,000	$ 66,736,000	$ 82,750,000
Granted, Shares						1,332,400
Shares remain eligible to vest						2,085,226
Common stock, shares reserved for future issuance						7,341,253	5,523,127
Stock-based compensation expense | $						$ 12,280,000	$ 5,825,000	$ 4,714,000
Granted, Weighted-Average Grant Date Fair Value | $ / shares						$ 8.47	$ 5.22	$ 6.07
Intrinsic value of options exercised | $						$ 2,689,563	$ 600,000	$ 2,000,000
Fair value of options vested | $						$ 5,600,000	4,600,000	3,200,000
2016 Inducement Award Program
Class of Stock [Line Items]
Maximum shares of common stock authorized to be issued						700,000
Granted, Shares						525,500
Shares remain eligible to vest						508,500
Common stock, shares reserved for future issuance						0
2016 Inducement Award Program | Employees
Class of Stock [Line Items]
Granted, Shares						525,500
Restricted Stock Units
Class of Stock [Line Items]
Granted shares of restricted stock	423,650					449,900
Stock-based compensation expense | $						$ 2,021,000	780,000	62,000
Granted, Weighted-Average Grant Date Fair Value | $ / shares						$ 10.34
Weighted average period of recognition for unrecognized compensation costs						1 year 10 months 28 days
Forfeited, Weighted-Average Grant Date Fair Value | $ / shares						$ 8.96
Unrecognized compensation cost | $						$ 4,000,000
Restricted Stock Units | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage						100.00%
Stock Options
Class of Stock [Line Items]
Shares issued	719,400
Stock-based compensation description						Options vest in installments of (i) 25% at the one year anniversary and (ii) in either 36 or 48 equal monthly installments beginning in the thirteenth month after the initial vesting commencement date or 12 equal quarterly installments beginning on the first day of each calendar quarter after the initial vesting commencement date or grant date, subject to the individual’s continuous service with the Company.
Options expiration after the date of grant						10 years
Stock-based compensation expense | $						$ 6,512,000	4,674,000	3,660,000
Stock Options | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage						25.00%
Restricted Stock
Class of Stock [Line Items]
Vesting periods			1 year
Stock-based compensation expense | $						$ 158,000	266,000	$ 909,000
Forfeited, Weighted-Average Grant Date Fair Value | $ / shares			$ 7.42			$ 7.42
Restricted stock requisite service period description						The awards of restricted stock contained a performance condition wherein the vesting commencement day was contingent upon the Company’s consummation of a liquidity event, as defined, prior to the fifth anniversary of the date of grant. Certain of the awards of restricted stock had a requisite service period that was complete upon grant. The remainder of the awards of restricted stock had a requisite service period of four years whereby the award vested 25% on the one year anniversary of a specified vesting commencement date, then ratably on the first day of each calendar quarter for 12 quarters, subject to continuous service by the individual and achievement of the performance target.
Grant-date fair value of restricted stock issued | $			$ 3,900,000
Award requisite service period			4 years
Unrecognized compensation cost | $						$ 0
Restricted Stock | Share Based Compensation Award Tranche One
Class of Stock [Line Items]
Vesting percentage			25.00%
Restricted Stock | Employees
Class of Stock [Line Items]
Granted shares of restricted stock			450,224
Restricted Stock | Non Employees
Class of Stock [Line Items]
Granted shares of restricted stock			79,067
Stock-based compensation expense | $						$ 132,154	$ 3,000
Common Stock
Class of Stock [Line Items]
Common stock, shares outstanding						47,612,619	38,615,709	30,662,218	20,370,624
Issuance of common stock, net of issuance costs, shares						8,672,270	7,865,293	10,083,070
Maximum | Restricted Stock Units
Class of Stock [Line Items]
Vesting periods						3 years
Maximum | Stock Options
Class of Stock [Line Items]
Vesting periods						48 months
Minimum | Restricted Stock Units
Class of Stock [Line Items]
Vesting periods						1 year
Minimum | Stock Options
Class of Stock [Line Items]
Vesting periods						12 months
At The Market Equity Offering Program | Common Stock
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs, shares						465,615	615,293
Proceeds from the issuance of common stock, net of issuance costs | $						$ 6,400,000	$ 5,700,000
At The Market Equity Offering Program | Common Stock | Scenario, Forecast
Class of Stock [Line Items]
Issuance of common stock, net of issuance costs, shares					694,306
Proceeds from the issuance of common stock, net of issuance costs | $					$ 10,500,000
At The Market Equity Offering Program | Maximum
Class of Stock [Line Items]
Common stock sales agreement amount | $				$ 75,000,000
2014 Plans
Class of Stock [Line Items]
Common stock, shares reserved for future issuance						1,790,600	1,140,328				1,785,000
Incremental rate at which the shares reserved for issuance increase						3.00%
2014 Plans | Employees
Class of Stock [Line Items]
Granted, Shares						719,400
2014 Plans | Director
Class of Stock [Line Items]
Granted, Shares						87,500
2014 Plans | Restricted Stock Units | Employees
Class of Stock [Line Items]
Granted shares of restricted stock						449,900
2014 Plans | Inducement Award Program
Class of Stock [Line Items]
Compensation not yet recognized, stock options | $						$ 13,000,000
Weighted average period of recognition for unrecognized compensation costs						2 years 8 months 19 days
2014 Employee Stock Purchase Plan
Class of Stock [Line Items]
Maximum shares of common stock authorized to be issued						262,500
Percentage of increase on common stock authorized on each anniversary						1.00%
Number of common stock outstanding						739,611
Common stock shares authorized percentage under the plan						5.00%
Purchase price at the end of offering period						85.00%
Offering period						6 months
Shares issued						44,789
Stock-based compensation expense | $						$ 200,000	$ 100,000