Outstanding Short Term Borrowings and Long Term Debt (Parenthetical) (Detail) (USD $)	1 Months Ended						9 Months Ended	1 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended
	May 02, 2011	Sep. 30, 2011 5.70% Senior Notes Interest rate swaps	Dec. 31, 2010 5.70% Senior Notes Interest rate swaps	Sep. 30, 2011 6.05% Subordinated Notes Interest rate swaps	Dec. 31, 2010 6.05% Subordinated Notes Interest rate swaps	May 02, 2011 Interest rate swaps	Sep. 30, 2011 5.375% Senior Notes	May 02, 2011 5.70% Senior Notes	Sep. 30, 2011 5.70% Senior Notes		May 02, 2011 6.05% Subordinated Notes	Sep. 30, 2011 6.05% Subordinated Notes		Sep. 30, 2011 3.875% Convertible Notes	Sep. 30, 2011 7.0% Junior Subordinated Debentures	Sep. 30, 2011 4.99% long-term notes payable
Debt Outstanding [Line Items]
Stated interest rate							5.375%		5.70%			6.05%		3.875%	7.00%	4.99%
Repurchases of principal amount of 5.70% Senior Notes and 6.05% Subordinated Notes	$ 312,600,000							$ 108,600,000			$ 204,000,000
Threshold for notional value of swaps						10,000,000
Fair value of the interest rate swap associated with the notes		$ 4,200,000	$ 15,700,000	$ 9,100,000	$ 36,300,000
Debt issuance																2009-04-30
Maturity							Sep. 15, 2020		Jun. 01, 2012	[1]		Jun. 01, 2017	[2]	Apr. 15, 2011	Oct. 15, 2033	Apr. 01, 2012

[1] At September 30, 2011 and December 31, 2010, included in the carrying value of our 5.70% Senior Notes are $4.2 million and $15.7 million, respectively, related to the fair value of the interest rate swap associated with the notes.

[2] At September 30, 2011 and December 31, 2010, included in the carrying value of our 6.05% Subordinated Notes are $9.1 million and $36.3 million, respectively, related to the fair value of the interest rate swap associated with the notes.