Subsequent Events - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended					1 Months Ended			1 Months Ended
	Apr. 30, 2009 Senior Notes due May 1, 2016	Apr. 17, 2006 Senior Notes due May 1, 2016	Sep. 30, 2013 Senior Notes due May 1, 2016	Sep. 30, 2013 Senior Notes due May 1, 2016 Semi Annual Payment, First Payment	Sep. 30, 2013 Senior Notes due May 1, 2016 Semi Annual Payment, Second Payment	Oct. 04, 2013 Subsequent Event 5.75% Senior Notes	Oct. 04, 2013 Subsequent Event 5.75% Senior Notes Semi Annual Payment, First Payment	Oct. 04, 2013 Subsequent Event 5.75% Senior Notes Semi Annual Payment, Second Payment	Oct. 04, 2013 Subsequent Event Senior Notes due May 1, 2016
Subsequent Event [Line Items]
Principal amount of senior notes		$ 125				$ 265
Interest rate stated on senior notes		7.00%				5.75%			7.00%
Senior notes due date		May 01, 2016				Oct. 15, 2023			May 01, 2016
Net proceeds from issuance of senior notes		123.5				263.0
Redemption of senior notes	7.0								115.0
Incurred charge for payment of call premium									$ 17.9
Effective interest rate			7.17%			5.84%
Interest payment date on senior notes				--05-01	--11-01		--04-15	--10-15
First Interest payment date						Apr. 15, 2014