Shareholders' Equity - Additional Information (Detail) (USD $)	1 Months Ended		3 Months Ended		12 Months Ended
	Feb. 28, 2011	Jan. 31, 2011	Mar. 31, 2011	Jun. 30, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Shareholders Equity [Line Items]
Company authorized to issue shares of preferred stock					20,000,000	20,000,000	20,000,000
Preferred stock, par value					$ 0.01	$ 0.01	$ 0.01
Preferred stock, Shares Issued
Public stock offering, shares, including underwriter's overallotment			3,450,000	5,175,000
Public stock offering, shares issued		3,000,000
Public stock offering transaction costs			$ 267,000	$ 522,000
Proceeds from the issuance of common stock, Value			$ 91,986,000	$ 108,205,000	$ 91,986,000	$ 108,205,000
Underwriter's over-allotment number of shares	450,000