Special Dividends - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended
	Dec. 31, 2012	Jan. 31, 2012	Dec. 14, 2012	Nov. 30, 2012	Nov. 12, 2012	Nov. 30, 2011
Dividends [Line Items]
Declared special dividend per share			$ 0.75	$ 0.75	$ 0.75	$ 0.75
Special dividends paid	$ 17.8	$ 17.5