Outstanding Short Term Borrowings and Long Term Debt (Detail) (USD $) In Thousands, unless otherwise specified					12 Months Ended			12 Months Ended					12 Months Ended					12 Months Ended		12 Months Ended			12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2011 5.375% Senior Notes	Dec. 31, 2010 5.375% Senior Notes	Sep. 30, 2010 5.375% Senior Notes	Dec. 31, 2011 5.70% Senior Notes		Dec. 31, 2010 5.70% Senior Notes		May 15, 2007 5.70% Senior Notes	Dec. 31, 2011 6.05% Subordinated Notes		Dec. 31, 2010 6.05% Subordinated Notes		May 15, 2007 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	Oct. 30, 2003 7.0% Junior Subordinated Debentures	Dec. 31, 2011 Other long-term debt		Dec. 31, 2010 Other short-term borrowings
Debt Outstanding [Line Items]
Maturity					Sep. 15, 2020			Jun. 01, 2012	[1]				Jun. 01, 2017	[2]				Apr. 15, 2011		Oct. 15, 2033			Apr. 01, 2012
Principal value					$ 350,000		$ 350,000	$ 141,429	[1]			$ 250,000	$ 45,964	[2]			$ 250,000	$ 250,000		$ 50,000		$ 51,500	$ 1,439	[3]
Short-term borrowings			37,245																						37,245	[4]
Senior Notes					347,793	347,601		143,969	[1]	265,613	[1]
Subordinated Notes													55,075	[2]	285,937	[2]
Convertible Notes																			249,304
Junior subordinated debentures																				55,372	55,548
Other long-term debt	1,439	[3]	5,257	[3]
Long-term debt	$ 603,648		$ 1,209,260

[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.

[3] Represents long-term notes payable related to one of our debt fund investments, and was payable beginning April 30, 2009 with the last payment due in April 2012.

[4] Represents cash collateral received from counterparties for our interest rate swap agreements related to our 5.70% Senior Notes and 6.05% Subordinated Notes. Due to the repurchase of $312.6 million of these notes and termination of associated portions of interest rate swaps in May 2011, the notional value of our swaps fell below the $10 million threshold specified in the agreement, and, therefore, the full collateral was returned to the counterparties.