The Company - Additional Information (Detail)			1 Months Ended	9 Months Ended
	Nov. 03, 2014 USD ($)	Sep. 30, 2014 USD ($)	Oct. 31, 2013 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) Segment shares	Sep. 30, 2014 USD ($)
Organization And Nature Of Business [Line Items]
Number of operating segments | Segment				1
Common stock initial public offering | shares			7,728,000
Net proceeds from initial public offering			$ 68,300,000
Underwriting discounts and commissions			5,400,000
Expenses for initial public offering			$ 3,600,000
Proceeds from issuance of convertible notes, net of discounts				$ 0	$ 124,375,000
Proceeds from sale of common stock				$ 47,100,000	0
Sale of stock, commissions, percentage of gross sales				3.00%
Convertible notes
Organization And Nature Of Business [Line Items]
Gross proceeds		$ 125,000,000		$ 125,000,000	125,000,000
Proceeds from issuance of convertible notes, net of discounts		124,100,000
Debt instrument, discounts and certain expenses		$ 875,000		$ 875,000	$ 875,000
IPO
Organization And Nature Of Business [Line Items]
Public offering price of the shares sold (in USD per share) | $ / shares			$ 10.00
Stock Offering Underwriter Over-Allotments Option
Organization And Nature Of Business [Line Items]
Common stock initial public offering | shares			1,008,000
Maximum
Organization And Nature Of Business [Line Items]
Shelf registration statement, aggregate dollar amount	$ 150,000,000.0
Cantor Fitzgerald and Co. | Common stock
Organization And Nature Of Business [Line Items]
Common stock issued and sold under sales agreement | shares				1,610,466
Cantor Fitzgerald and Co. | Common stock | Maximum
Organization And Nature Of Business [Line Items]
Shelf registration statement, aggregate dollar amount	$ 50,000,000