Earnings per share - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended
	Aug. 26, 2011	Sep. 30, 2012	Sep. 30, 2012	Sep. 01, 2011	Apr. 29, 2011
Class of Warrant or Right [Line Items]
Conversion price for the preferred stock	$ 12.00		$ 12.00
Commitment public underwritten offering of equity securities closing days			180 days
Equity securities resulting in gross proceeds			$ 15.0
Gross proceeds			$ 5.0
Effective price per share	12.00	12.00	12.00
Shares of its common stock issued pursuant to additional shares			50.00%
Anti-dilutive potential common shares			736,252
Exercise price per share			$ 13.00
Company estimated the average fair value		$ 11.71	$ 11.71
Strike price of dilutive common shares for SAR			$ 22.07
Shares of common stock issuable upon exercise of the Roth Warrant				105,000	3,360,000
Reverse Split [Member]
Class of Warrant or Right [Line Items]
Exercise price per share			$ 13.00
Roth Warrant [Member]
Class of Warrant or Right [Line Items]
Shares of common stock issuable upon exercise of the Roth Warrant		62,116	62,116	62,116
Private Placement Warrants [Member]
Class of Warrant or Right [Line Items]
Shares issued for warrants exercised		13,750