Subsequent event - Additional Information (Detail) (Subsequent Event [Member], USD $)	1 Months Ended
	Jul. 16, 2013
Subsequent Event [Line Items]
Public offering proceeds used for the repayment of debt	$ 25,000,000
Underwritten Public Offering [Member]
Subsequent Event [Line Items]
Public offering shares	2,005,000
Underwritten public offering Price per share	$ 35.00
Shares sold through Public offering	1,050,000
Share sold by stock holders through public offering.	955,000
Proceeds to the company from Public offering	34,530,250
Public offering expense	$ 200,000