Shareholders' Equity - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			1 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Maximum	Oct. 25, 2012 Subsequent Event Dividend Declared
Stockholders Equity Note [Line Items]
Repurchase and retirement of common stock			$ 58,978,000
Repurchase and retirement of common stock, shares			813,000
Number of shares authorized to repurchase					2,816,000
Cash Dividends Declared And Paid Per Common Share	$ 0.370	$ 0.225	$ 1.110	$ 0.675
Cash dividend paid, payment date	Sep. 17, 2012					Dec. 17, 2012
Cash dividend paid, record date	Aug. 31, 2012					Nov. 30, 2012
Cash dividend declared						$ 0.37
Cash dividend declared, date						Oct. 25, 2012
Common stock excluded from calculation of diluted earnings per share	917,000	44,000	1,148,000	530,000