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Number of additional shares authorized for issuance under an established share-based compensation plan.

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Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.

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Stockholders' Equity - Additional Information (Detail) - USD ($)						1 Months Ended		12 Months Ended
	Jan. 01, 2016	Apr. 07, 2015	Jan. 11, 2015	Jan. 01, 2015	Sep. 30, 2013	Sep. 30, 2013	Nov. 30, 2009	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2010	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares sold					6,772,221
Overallotment option granted to the underwriters					883,333
Common stock purchase price					$ 18.00	$ 18.00
Net proceeds received from IPO					$ 110,381,000
Conversion of redeemable convertible preferred stock into common stock, shares								17,128,024
Common stock, shares outstanding								35,281,001	34,513,845
Voting right of common stockholders								one vote per share
Preferred stock, shares outstanding								0
Stock-based compensation expense								$ 19,524,000	$ 11,176,000	$ 5,989,000
Total shares of common stock available for issuance								5,750,917	5,137,121
2010 Stock Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock								1,162,500
Common stock available for issuance												4,232,500
2013 Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of common stock								1,355,171
Common stock available for issuance								512,568
Increase in shares available for issuance	1,380,949			1,134,996
Percentage increase in shares available for issuance								4.00%
Total shares of common stock available for issuance								2,398,031	1,694,077
2010 and 2013 Stock Incentive Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted period								4 years
Options are exercisable from date of grant for a period								10 years
2013 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock available for issuance								788,503	788,503
Unvested Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense								$ 0	$ 0	0
Fair value of restricted stock								$ 0	$ 0	78,000
Total shares of common stock available for issuance								1,297,054	969,758
Unvested Restricted Stock [Member] \| 2010 and 2013 Stock Incentive Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense								$ 16,072,000	$ 5,615,000	740,000
Common Stock Options Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock available for issuance								1,267,329	1,684,783
Common Stock Options Outstanding [Member] \| 2010 and 2013 Stock Incentive Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense								$ 3,452,000	$ 5,561,000	$ 5,249,000
Weighted-average fair value of options granted								$ 11.00	$ 26.67	$ 15.88
Aggregate intrinsic value of stock options exercised								$ 2,758,000	$ 42,325,000	$ 4,799,000
Unrecognized compensation cost								$ 27,867,000
Amount to be recognized over weighted-average periods								1 year 10 months 24 days
Common Stock Options Outstanding [Member] \| 2013 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock available for issuance					788,503	788,503
Description of customary employment								more than 20 hours a week
Percentage of voting power						5.00%
Percentage of eligible compensation						10.00%
Percentage of fair market value of common stock						85.00%
Common Stock Options Outstanding [Member] \| 2013 Employee Stock Purchase Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock value					$ 25,000	$ 25,000
Founders [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares sold							2,125,000				112,500
Roche [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares sold		5,000,000	5,000,000
Common stock purchase price		$ 50.00	$ 50.00
Primary investment in cash		$ 250,000,000	$ 250,000,000
Common stock, shares outstanding		15,604,288	15,604,288