Common Stock Reserved for Issuance - Schedule of Common Stock Reserved for Issuance (Detail) - shares	Jun. 30, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved for future issuance	22,126,461	22,154,290
Outstanding Preferred Stock Warrants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved for future issuance	885,201	976,492
Series A Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved for future issuance	252,817	252,817
Series B Redeemable Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved for future issuance	1,947,354	1,947,354
Series B-1 Redeemable Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved for future issuance	1,478,328	1,392,300
Series C Redeemable Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved for future issuance	2,493,017	2,487,770
Series D Redeemable Convertible Preferred Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved for future issuance	11,409,360	11,409,360
Outstanding And Issued Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved for future issuance	3,294,849	2,138,096
Shares Reserved For Future Option Grants [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total common stock reserved for future issuance	365,535	1,550,101