Subsequent Events (Details) - USD ($)				1 Months Ended						3 Months Ended
	May 11, 2017	May 09, 2017	May 03, 2017	Jun. 30, 2017	May 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Feb. 29, 2016	Sep. 30, 2013	Mar. 31, 2017	Jul. 31, 2016	Mar. 31, 2016	Apr. 30, 2017	Apr. 21, 2017	Dec. 31, 2016	Aug. 29, 2016
Subsequent Events
Number of shares authorized										38,000,000					38,000,000
Common stock, par value (in dollars per share)										$ 0					$ 0
Preferred stock, shares authorized										11,242,172					11,242,172
Preferred stock, par value (in dollars per share)										$ 0					$ 0
Issuance of common shares								429,000			1,090,500
Issuance price per share							$ 7.70	$ 7.00			$ 7.70
Net proceeds from issuance of shares, after deducting underwriting discounts and commissions and other offering expenses					$ 176,367,000
Other offering expenses								$ 23,000		$ 2,049,000	$ 97,000	$ 23,000
Cash payment for purchase of equity method investment										$ 1,624,000
2014 Equity Incentive Plan
Subsequent Events
Number of shares granted										553,886		1,034,805
Subsequent Event
Subsequent Events
Number of shares authorized	200,000,000												50,000,000	50,000,000
Common stock, par value (in dollars per share)	$ 0
Preferred stock, shares authorized	10,000,000
Preferred stock, par value (in dollars per share)	$ 0
Aggregate net proceeds from the IPO and underwriters issuance	$ 176,367,000
Subsequent Event | Initial public offering
Subsequent Events
Issuance of common shares		9,900,000
Issuance price per share		$ 17.00
Net proceeds from issuance of shares, after deducting underwriting discounts and commissions and other offering expenses		$ 152,889,000
Other offering expenses		3,630,000
Underwriting discounts and commissions		$ 11,781,000
Convertible preferred stock converted into shares of common stock		9,358,560
Remaining unamortized portion of BCF reclassified to additional paid-in-capital		$ 8,006,000
Fair value of contingent equity liabilities					32,020,000
Repayment of principal amount to related party					595,000.000
Repayment of interest amount to related party					$ 9,000
Subsequent Event | Over allotment option
Subsequent Events
Issuance of common shares	1,485,000
Net proceeds from issuance of shares, after deducting underwriting discounts and commissions and other offering expenses	$ 23,478,000
Aggregate net proceeds from the IPO and underwriters issuance	176,367,000
Net proceeds from underwriting	23,478,000
Underwriting discounts and commissions	$ 1,767,000
Subsequent Event | Over allotment option | BMS and AstraZenca
Subsequent Events
Issuance of common shares	1,883,523	1,883,523
Common shares value issued	$ 0
Subsequent Event | 2017 Equity Incentive Plan
Subsequent Events
Number of shares reserved for issuance			7,611,971
Number of shares granted			2,712,741
Percentage of common stock issued that can be increased			4.00%
Subsequent Event | 2014 Equity Incentive Plan
Subsequent Events
Number of shares granted			372
Subsequent Event | 2017 Employee Share Purchase Plan
Subsequent Events
Number of shares reserved for issuance			339,139
Minimum number of issued shares that can be increased			600,000
Percentage of common stock issued that can be increased			1.00%
Product related collaborative arrangements | BMS Agreement
Subsequent Events
Issuance of common shares					1,345,374
Issuance price per share							$ 9.2911				$ 9.2911
Common shares value issued							$ 12,500,000
Product related collaborative arrangements | AstraZeneca
Subsequent Events
Issuance of common shares					538,149
Issuance price per share						$ 9.2911
Common shares value issued						$ 5,000,000
Product related collaborative arrangements | Subsequent Event | Initial public offering | BMS Agreement
Subsequent Events
Issuance of common shares					1,345,374
Product related collaborative arrangements | Subsequent Event | Initial public offering | AstraZeneca
Subsequent Events
Issuance of common shares					538,149
Collaborative arrangement | Yale Agreement
Subsequent Events
Issuance of common shares									250,000
Kleo
Subsequent Events
Shares purchased in equal tranches										1,375,000						1,375,000
Cash payment for purchase of equity method investment										$ 1,976,000
Kleo | Subsequent Event
Subsequent Events
Shares purchased in equal tranches				1,375,000
Cash payment for purchase of equity method investment				$ 1,375,000