Notes payable (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Debt Instrument [Line Items]
Others	$ 23,294		$ 23,496
Notes Payable	1,506,408		1,584,754
Fixed Rate 027 To 419 Percent Advances Due 2015 To 2021 [Member]
Debt Instrument [Line Items]
Federal Home Loan Bank Advances Long Term	510,825		589,229
Fixed Rate 747 Percent Term Notes Due 2014 [Member]
Debt Instrument [Line Items]
Notes Payable	675		675
Floating Rate 300 Percent Term Notes Due in 2014 [Member]
Debt Instrument [Line Items]
Notes Payable	10	[1]	14	[1]
Fixed Rate 6125 To 8327 Percent Junior Subordinated Deferrable Interest Debentures Due 2027 To 2034 [Member]
Debt Instrument [Line Items]
Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust	439,800		439,800
Fixed Rate 500 Percent Until December 2013 And 900 Percent Thereafter Junior Subordinated Deferrable Interest Debentures With No Stated Maturity [Member]
Debt Instrument [Line Items]
Junior Subordinated Debenture Owed To Unconsolidated Subsidiary Trust	$ 531,804	[2]	$ 531,540	[2]

[1] The 10-year U.S. Treasury note key index rate at March 31, 2014 and December 31, 2013 was 2.72% and 3.03%, respectively.

[2] The debentures are perpetual and may be redeemed by the Corporation at any time, subject to the consent of the Board of Governors of the Federal Reserve System. The discount on the debentures is being amortized over an estimated 30-year term that started in August 2009. The effective interest rate, including the discount accretion, was approximately 16% at March 31, 2014 and December 31, 2013.