Subsequent Events - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended	6 Months Ended	12 Months Ended
	Jul. 21, 2015	Jul. 10, 2015	Jun. 30, 2015	Jun. 30, 2015	Dec. 31, 2014	Jul. 15, 2015	Jul. 14, 2015	Jun. 24, 2008
Subsequent Event [Line Items]
Preferred stock warrants exercised					0
Cash proceeds from warrants exercised				$ 0.3
Number of common stock shares reserved for issuance			22,126,461	22,126,461	22,154,290
Amended and restated common stock authorized			180,000,000	180,000,000	180,000,000
Amended and restated preferred stock authorized			136,074,466	136,074,466	135,913,741
Performance-Based Stock Option Grant [Member]
Subsequent Event [Line Items]
Additional stock-based compensation related to stock options				$ 0.1
2008 Plan [Member]
Subsequent Event [Line Items]
Maximum number of common stock shares allowed to issue under employee stock purchase plan								308,725
Series B and B-1 Redeemable Convertible Preferred Stock [Member]
Subsequent Event [Line Items]
Accruing dividends			$ 5.5	$ 5.5
Subsequent Event [Member]
Subsequent Event [Line Items]
Preferred stock warrants exercised	493,648
Cash proceeds from warrants exercised		$ 1.2
Number of common stock shares issued upon exercise of preferred stock warrants	390,680
IPO price per share	$ 17
Amended and restated common stock authorized	500,000,000
Amended and restated preferred stock authorized	10,000,000
Subsequent Event [Member] | Executive officer [Member] | Performance-Based Stock Option Grant [Member]
Subsequent Event [Line Items]
Additional stock-based compensation related to stock options	$ 0.1
Subsequent Event [Member] | 2008 Plan [Member]
Subsequent Event [Line Items]
Number of common stock shares reserved for issuance	365,535
Subsequent Event [Member] | 2015 Equity Incentive Plan [Member]
Subsequent Event [Line Items]
Number of common stock shares reserved for issuance							3,400,000
Subsequent Event [Member] | 2015 Employee Stock Purchase Plan [Member]
Subsequent Event [Line Items]
Number of common stock shares reserved for issuance						700,000
Maximum number of common stock shares allowed to issue under employee stock purchase plan						3,400,000
Subsequent Event [Member] | Series B and B-1 Redeemable Convertible Preferred Stock [Member]
Subsequent Event [Line Items]
Accruing dividends	$ 5.5
Subsequent Event [Member] | Series C and D Redeemable Convertible Preferred Stock [Member]
Subsequent Event [Line Items]
Accruing dividends	$ 3.9
Number of common stock shares issued to preferred stockholders in payment of cumulative accrued dividends	750,946
Series B-1 Preferred Stock Warrants, Expiration June 30, 2018 [Member]
Subsequent Event [Line Items]
Preferred stock warrants exercised			3,079	3,079
Warrants exercise price			$ 7.4500	$ 7.4500
Series B-1 Preferred Stock Warrants, Expiration June 30, 2018 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Preferred stock warrants exercised		28,699
Warrants exercise price		$ 7.4500
Series B-1 Preferred Stock Warrants, Expiration Various Dates In 2016 - 2021 [Member]
Subsequent Event [Line Items]
Preferred stock warrants exercised			82,949	82,949
Warrants exercise price			$ 2.6075	$ 2.6075
Series B-1 Preferred Stock Warrants, Expiration Various Dates In 2016 - 2021 [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Preferred stock warrants exercised		329,559
Warrants exercise price		$ 2.6075
Series C Preferred Stock Warrants [Member]
Subsequent Event [Line Items]
Preferred stock warrants exercised			5,247	5,247
Warrants exercise price			$ 5.2150	$ 5.2150
Series C Preferred Stock Warrants [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Preferred stock warrants exercised		32,138
Warrants exercise price		$ 5.2150