The Company - Additional Information (Detail) (USD $)	0 Months Ended	1 Months Ended	3 Months Ended
	Mar. 31, 2015	Oct. 31, 2013	Mar. 31, 2015	Mar. 31, 2014	Sep. 30, 2014
Organization And Nature Of Business [Line Items]
Common stock initial public offering		7,728,000
Public offering price of the shares sold		$ 10.00
Net proceeds from initial public offering		$ 68,300,000
Underwriting discounts and commissions		5,400,000
Payments of stock issuance costs			1,000,000
Expenses for initial public offering		3,600,000
Common stock issued and sold under sales agreement	1,204,248
Proceeds from sale of common stock			35,000,000	0
Convertible notes
Organization And Nature Of Business [Line Items]
Gross proceeds	125,000,000		125,000,000
Net proceeds from issuance of debt			124,100,000
Debt instrument, discounts and certain expenses	875,000		875,000		875,000
Stock Offering Underwriter Over-Allotments Option
Organization And Nature Of Business [Line Items]
Common stock initial public offering		1,008,000
Maximum
Organization And Nature Of Business [Line Items]
Shelf registration statement, aggregate dollar amount			150,000,000
Cantor Fitzgerald and Co. | Common stock | Maximum
Organization And Nature Of Business [Line Items]
Shelf registration statement, aggregate dollar amount			$ 50,000,000