Outstanding Short Term Borrowings and Long Term Debt (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012		Dec. 31, 2011
Debt Outstanding [Line Items]
Principal value	$ 0	[1]
Short-term borrowings	508,170		0
Other long-term debt	0	[1]	1,439	[1]
Total long-term debt	458,314		603,648
Federal Home Loan Bank Advances
Debt Outstanding [Line Items]
Maturity	Oct. 01, 2012
Principal value	215,000
Short-term borrowings	215,000		0
Federal Funds Purchased
Debt Outstanding [Line Items]
Maturity	Oct. 01, 2012
Principal value	287,000
Short-term borrowings	287,000		0
Other short-term borrowings
Debt Outstanding [Line Items]
Principal value	6,170	[2]
Short-term borrowings	6,170	[2]	0	[2]
5.375% Senior Notes
Debt Outstanding [Line Items]
Maturity	Sep. 15, 2020
Principal value	350,000
Senior Notes	347,944		347,793
5.70% Senior Notes
Debt Outstanding [Line Items]
Maturity	Jun. 01, 2012	[3]
Principal value	0
Senior Notes	0		143,969	[3]
6.05% Subordinated Notes
Debt Outstanding [Line Items]
Maturity	Jun. 01, 2017	[4]
Principal value	45,964	[4]
Subordinated Notes	55,130	[4]	55,075	[4]
7.0% Junior Subordinated Debentures
Debt Outstanding [Line Items]
Maturity	Oct. 15, 2033
Principal value	50,000
Junior Subordinated Debentures	$ 55,240		$ 55,372

[1] Represents long-term notes payable related to one of our debt fund investments. The last payment related to the notes was made in April 2012.

[2] Represents cash collateral received from our counterparty for our interest rate swap agreement related to our 6.05% Subordinated Notes.

[3] At December 31, 2011, included in the carrying value of our 5.70% Senior Notes was $2.6 million related to the fair value of the interest rate swap associated with the notes.

[4] At September 30, 2012 and December 31, 2011, included in the carrying value of our 6.05% Subordinated Notes were $9.5 million and $8.8 million, respectively, related to the fair value of the interest rate swap associated with the notes.