Stock Compensation Plans - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands				9 Months Ended
	Apr. 16, 2015	Mar. 31, 2014	Feb. 12, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant				1,057,080
Release of repurchase liability for shares vested				$ 70	$ 78
Weighted-average grant date fair value of stock options granted (usd per share)				$ 15.35	$ 11.08
Fair value of common stock (usd per share)		$ 11.30	$ 7.55			$ 5.93
Compensation cost related to unvested employee stock option awards				$ 5,500
Remaining weighted-average vesting period				1 year 8 months 27 days
IPO by April 15, 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount for lack of marketability		2.00%
Private Company [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount for lack of marketability		27.00%	28.00%
IPO by May 15, 2014 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount for lack of marketability			8.00%
Non-Employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost related to unvested employee stock option awards				$ 92
Remaining weighted-average vesting period				1 year 10 months 2 days
Sale [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount for lack of marketability		17.00%	20.00%
Two Thousand And Fourteen Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grants under Equity Incentive Plans, term				10 years
Option vesting under Equity Incentive Plans, term				4 years
Shares of common stock for annual increase in shares available for issuance				1,200,000
Percentage of outstanding shares of common stock for annual increase in shares available for issuance				3.00%
Increase in number of shares available for issuance	720,369
Shares available for grant				1,057,080
Two Thousand Twelve Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option grants under Equity Incentive Plans, term				10 years
Option vesting under Equity Incentive Plans, term				4 years
Common stock exercised				74,970
Unvested common stock options exercised in the period				19,454
Increase to repurchase liability in the period				$ 8
Common stock options vested in the period				15,537
Release of repurchase liability for shares vested				$ 78
Stock option repurchase liability				$ 54