Stockholders' Equity - Additional Information (Detail) - USD ($)						1 Months Ended		12 Months Ended
	Apr. 07, 2015	Jan. 11, 2015	Jan. 01, 2015	Jan. 01, 2014	Sep. 30, 2013	Sep. 30, 2013	Nov. 30, 2009	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2010
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								34,513,845	28,223,958
Voting right of common stockholders								One vote per share
Preferred stock, shares outstanding								0	0
Stock-based compensation expense								$ 11,176,000	$ 5,989,000	$ 7,316,000
Total shares of common stock available for issuance								5,137,121	5,292,012
2013 Stock Incentive 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			1,134,996	1,125,921
Percentage increase in shares available for issuance								4.00%
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
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
Unvested Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense								$ 0	$ 0	$ 5,764,000
Fair value of restricted stock								$ 0	$ 78,000	5,943,000
Total shares of common stock available for issuance								969,758	335,933
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								$ 5,615,000	$ 740,000	153,000
Shares remaining from early exercise of stock options								9,894
Common Stock Options Outstanding [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total shares of common stock available for issuance								1,684,783	2,792,021
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								$ 5,561,000	$ 5,249,000	$ 1,399,000
Shares remaining from early exercise of stock options								9,894	116,316	8,750
Weighted-average fair value of options granted								$ 26.67	$ 15.88	$ 4.89
Aggregate intrinsic value of stock options exercised								$ 42,325,000	$ 4,799,000	$ 791,000
Unrecognized compensation cost								$ 27,946,000
Amount to be recognized over weighted-average periods								2 years 1 month 6 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
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
Founders [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock shares sold							2,125,000				112,500