Notes Payable (Parenthetical) (Detail) (USD $) In Thousands, unless otherwise specified				6 Months Ended		3 Months Ended							3 Months Ended
	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010	Jun. 30, 2011 Federal Deposit Insurance Corporation	Apr. 30, 2010 Federal Deposit Insurance Corporation	Jun. 30, 2011 Federal Deposit Insurance Corporation Fixed Rate 2.50 Percent Notes Due April 2015	Dec. 31, 2010 Federal Deposit Insurance Corporation Fixed Rate 2.50 Percent Notes Due April 2015	Jun. 30, 2010 Federal Deposit Insurance Corporation Fixed Rate 2.50 Percent Notes Due April 2015	Jun. 30, 2011 Fixed Rate 0.66 to 4.95 Percent Advances Due 2011 to 2021	Dec. 31, 2010 Fixed Rate 0.66 to 4.95 Percent Advances Due 2011 to 2021	Jun. 30, 2010 Fixed Rate 0.66 to 4.95 Percent Advances Due 2011 to 2021	Jun. 30, 2010 Fixed Rate 5.10 Percent Advances Due 2010	Jun. 30, 2011 Fixed Rate 5.25 to 7.86 Percent Term Notes Due 2012 to 2016	Dec. 31, 2010 Fixed Rate 5.25 to 7.86 Percent Term Notes Due 2012 to 2016	Jun. 30, 2010 Fixed Rate 5.25 to 7.86 Percent Term Notes Due 2012 to 2016	Jun. 30, 2011 Floating Rate 3.00 Percent Term Notes Due 2011 to 2013	Dec. 31, 2010 Floating Rate 3.00 Percent Term Notes Due 2011 to 2013	Jun. 30, 2010 Floating Rate 3.00 Percent Term Notes Due 2011 to 2013	Jun. 30, 2010 Floating Rate 9.75 Percent Term Notes Due 2011	Jun. 30, 2011 Fixed Rate 6.125 to 8.327 Percent Junior Subordinated Deferrable Interest Debentures Due 2027 to 2034	Dec. 31, 2010 Fixed Rate 6.125 to 8.327 Percent Junior Subordinated Deferrable Interest Debentures Due 2027 to 2034	Jun. 30, 2010 Fixed Rate 6.125 to 8.327 Percent Junior Subordinated Deferrable Interest Debentures Due 2027 to 2034	Jun. 30, 2011 Fixed Rate 5.00 Percent Until December 2013 And 9.00 Percent Thereafter Junior Subordinated Deferrable Interest Debentures with no Stated Maturity	Dec. 31, 2010 Fixed Rate 5.00 Percent Until December 2013 And 9.00 Percent Thereafter Junior Subordinated Deferrable Interest Debentures with no Stated Maturity	Jun. 30, 2010 Fixed Rate 5.00 Percent Until December 2013 And 9.00 Percent Thereafter Junior Subordinated Deferrable Interest Debentures with no Stated Maturity	Jun. 30, 2011 Three Month LIBOR	Jun. 30, 2010 Three Month LIBOR
Debt Instrument [Line Items]
Advances with the FHLB, earliest maturity									2011	2011	2011
Advances with the FHLB, latest maturity									2021	2016	2016
Advances with the FHLB, interest rate range from									0.66%	0.66%	1.48%
Advances with the FHLB, interest rate range to									4.95%	4.95%	5.10%
Advances with the FHLB, maturity												2010
Advances with the FHLB, interest rate	0.35%	0.35%										5.10%
Notes payable, gross																							$ 936,000	$ 936,000	$ 936,000
Notes payable, maturity date range start													2012	2012	2012	2011	2011	2011		2027	2027	2027
Notes payable, unamortized premium						1,202	1,202	1,202
Notes payable, maturity date																			2011
Notes payable, unamortized premium	$ 478,995																						$ 478,995	$ 491,000	$ 502,113
Notes payable, maturities				five years from issuance (April 30, 2015), or such date as such amount may become due and payable pursuant to the terms of the note																			no stated maturity	no stated maturity	no stated maturity
Notes payable, maturity date range end						2015-04-30	2015-04-30	2015-04-30					2016	2016	2016	2013	2013	2013		2034	2034	2034
Notes payable, interest rate range maximum													5.25%	5.25%	5.25%					6.125%	6.125%	6.125%
Notes payable, interest rate					2.50%	2.50%	2.50%	2.50%
Notes payable, interest rate range maximum													7.86%	7.86%	13.00%					8.327%	8.327%	8.327%
Notes payable, interest rate				Borrowings under the note bear interest at an annual fixed rate of 2.50% and are paid monthly. If the Corporation fails to pay any interest as and when due, such interest shall accrue interest at the note interest rate plus 2.00% per annum												paying interest monthly at a floating rate of 3.00% over the 10-year U.S. Treasury note rate	paying interest monthly at a floating rate of 3.00% over the 10-year U.S. Treasury note rate	paying interest monthly at a floating rate of 3.00% over the 10-year U.S. Treasury note rate	paying interest quarterly at a floating rate of 9.75% over the 3-month LIBOR rate				a fixed interest rate of 5.00% until, but excluding December 5, 2013 and 9.00% thereafter	a fixed interest rate of 5.00% until, but excluding December 5, 2013 and 9.00% thereafter	a fixed interest rate of 5.00% until, but excluding December 5, 2013 and 9.00% thereafter
Key index rates, 3-month LIBOR rate																										0.25%	0.53%
Key index rates, 10-year U.S. Treasury note	3.16%		2.93%