Notes payable (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Jun. 30, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Others	$ 22,892			$ 23,496
Notes Payable	1,723,573			1,584,754
Fixed Rate 027 To 419 Percent Advances Due 2014 To 2021 [Member]
Debt Instrument [Line Items]
Federal Home Loan Bank Advances Long Term	810,202			589,229
Fixed Rate 700 Percent Notes Due July 2019 [Member]
Debt Instrument [Line Items]
Senior Long Term Notes	450,000		450,000	0
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	4	[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	$ 0	[2]		$ 531,540	[2]

[1] The 10-year U.S. Treasury note key index rate at September 30, 2014 and December 31, 2013 was 2.49% 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 was being amortized over an estimated 30-year term that started in August 2009. During the quarter ended June 30, 2014, in connection with the repayment of these Notes completed on July 2, 2014, the Corporation accelerated the related amortization of the discount and deferred costs amounting to $414.1 million, which is reflected as interest expense in the consolidated statement of operations. The effective interest rate, including the discount accretion, was approximately 16% at December 31, 2013.