Subsequent Events - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	12 Months Ended		1 Months Ended
	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2012 Restricted Stock	Feb. 28, 2013 Performance Shares Issued To Officers Restricted Stock	Feb. 28, 2013 Performance Shares Issued To Officers Restricted Stock Other Employees	Feb. 28, 2013 Performance Shares Issued To Officers Restricted Stock Units (RSUs) Officers and executive officers	Feb. 28, 2013 Dividend Declared
Subsequent Event [Line Items]
Number of shares issued			349,000	400,000	100,000	300,000
Aggregate value of shares issued				$ 15.0
Vesting period						3 years
Dividend declared per common share	$ 0.20	$ 0.60					$ 0.53
Dividend payable date							Apr. 15, 2013
Dividend declared, record date							Apr. 03, 2013