Significant Accounting Policies - Summary of Potentially Dilutive Securities (Detail) - shares	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Warrants to purchase common stock	148,444	159,049
Unvested early exercise options	1,387,580	2,195,754
Options to purchase common stock	5,900,011	4,087,906
Total	7,436,035	6,442,709