Outstanding Short Term Borrowings and Long Term Debt (Parenthetical) (Detail) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended			12 Months Ended		12 Months Ended		12 Months Ended
	Dec. 31, 2010	Dec. 31, 2011 5.375% Senior Notes	Dec. 31, 2010 5.375% Senior Notes	May 02, 2011 5.70% Senior Notes	Dec. 31, 2011 5.70% Senior Notes		Dec. 31, 2010 5.70% Senior Notes	May 02, 2011 6.05% Subordinated Notes	Dec. 31, 2011 6.05% Subordinated Notes		Dec. 31, 2010 6.05% Subordinated Notes	Dec. 31, 2011 3.875% Convertible Notes	Dec. 31, 2010 3.875% Convertible Notes	Dec. 31, 2011 7.0% Junior Subordinated Debentures	Dec. 31, 2010 7.0% Junior Subordinated Debentures	Dec. 31, 2011 Other long-term debt	Dec. 31, 2010 Interest rate swaps	Dec. 31, 2011 Interest rate swaps 5.70% Senior Notes	Dec. 31, 2010 Interest rate swaps 5.70% Senior Notes	Dec. 31, 2011 Interest rate swaps 6.05% Subordinated Notes	Dec. 31, 2010 Interest rate swaps 6.05% Subordinated Notes
Debt Outstanding [Line Items]
Stated interest rate		5.375%	5.375%		5.70%		5.70%		6.05%		6.05%		3.875%	7.00%	7.00%
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																		$ 2,600,000	$ 15,700,000	$ 8,800,000	$ 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 December 31, 2011 and 2010, included in the carrying value of our 5.70% Senior Notes are $2.6 million and $15.7 million, respectively, related to the fair value of the interest rate swap associated with the notes.

[2] At December 31, 2011 and 2010, included in the carrying value of our 6.05% Subordinated Notes are $8.8 million and $36.3 million, respectively, related to the fair value of the interest rate swap associated with the notes.