Outstanding Short Term Borrowings and Long Term Debt (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified	0 Months Ended	12 Months Ended		12 Months Ended		3 Months Ended					12 Months Ended					12 Months Ended
	Apr. 15, 2011 3.875% Convertible Notes	Dec. 31, 2012 3.875% Convertible Notes	Dec. 31, 2011 3.875% Convertible Notes	Dec. 31, 2012 5.375% Senior Notes	Dec. 31, 2011 5.375% Senior Notes	Jun. 30, 2012 5.70% Senior Notes		Dec. 31, 2012 5.70% Senior Notes	Dec. 31, 2011 5.70% Senior Notes	Dec. 31, 2011 5.70% Senior Notes Interest rate swaps	Dec. 31, 2012 6.05% Subordinated Notes		Dec. 31, 2011 6.05% Subordinated Notes	Dec. 31, 2012 6.05% Subordinated Notes Interest rate swaps	Dec. 31, 2011 6.05% Subordinated Notes Interest rate swaps	Dec. 31, 2012 7.0% Junior Subordinated Debentures	Dec. 31, 2011 7.0% Junior Subordinated Debentures
Debt Outstanding [Line Items]
Stated interest rate		3.875%	3.875%	5.375%	5.375%			5.70%	5.70%		6.05%		6.05%			7.00%	7.00%
Fair value of the interest rate swap associated with the notes									$ 2,600	$ 2,600	$ 9,000		$ 8,800	$ 9,000	$ 8,800
Maturity	Apr. 15, 2011	Apr. 15, 2011		Sep. 15, 2020		Jun. 01, 2012	[1]				Jun. 01, 2017	[2]				Oct. 15, 2033

[1] At December 31, 2011, included in the carrying value of our 5.70% Senior Notes was $2.6 million related to hedge accounting associated with the notes.

[2] At December 31, 2012 and 2011, included in the carrying value of our 6.05% Subordinated Notes were $9.0 million and $8.8 million, respectively, related to hedge accounting associated with the notes.