Loans Part 1 (Details) (USD $)																				6 Months Ended
	Jun. 30, 2012		Dec. 31, 2011		Jun. 30, 2011		Jun. 30, 2012 Commercial [Member]	Dec. 31, 2011 Commercial [Member]	Jun. 30, 2011 Commercial [Member]	Jun. 30, 2012 Commercial [Member] Energy [Member]	Jun. 30, 2012 Commercial [Member] Services [Member]	Jun. 30, 2012 Commercial Real Estate [Member]	Dec. 31, 2011 Commercial Real Estate [Member]	Jun. 30, 2011 Commercial Real Estate [Member]	Jun. 30, 2012 Residential Mortgage [Member]	Dec. 31, 2011 Residential Mortgage [Member]	Jun. 30, 2011 Residential Mortgage [Member]	Jun. 30, 2012 Residential Mortgage [Member] Permanent Residential Mortgage [Member]	Jun. 30, 2012 Residential Mortgage [Member] Permanent Mortgages Guaranteed by US Government Agencies [Member]	Jun. 30, 2012 Residential Mortgage [Member] Home Equity [Member]	Jun. 30, 2012 Consumer [Member]	Dec. 31, 2011 Consumer [Member]	Jun. 30, 2011 Consumer [Member]
Loan receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	$ 6,309,425,000		$ 6,050,429,000		$ 5,530,343,000		$ 3,536,199,000	$ 3,261,344,000	$ 2,847,559,000			$ 864,077,000	$ 896,820,000	$ 868,513,000	$ 1,708,252,000	$ 1,646,554,000	$ 1,517,676,000				$ 200,897,000	$ 245,711,000	$ 296,595,000
Loans receivables with variable rate of interest	5,122,524,000		5,018,028,000		5,007,031,000		3,481,816,000	3,224,915,000	3,269,321,000			1,181,923,000	1,295,290,000	1,209,155,000	274,118,000	298,206,000	322,585,000				184,667,000	199,617,000	205,970,000
Loan receivable non-accrual	144,482,000		201,286,000		200,170,000		34,529,000	68,811,000	53,365,000			80,214,000	99,193,000	110,363,000	22,727,000	29,767,000	31,693,000				7,012,000	3,515,000	4,749,000
Total	11,576,431,000		11,269,743,000		10,737,544,000		7,052,544,000	6,555,070,000	6,170,245,000	2,200,000,000	1,900,000,000	2,126,214,000	2,291,303,000	2,188,031,000	2,005,097,000	1,974,527,000	1,871,954,000			696,000,000	392,576,000	448,843,000	507,314,000
Accruing loans past due (90 days)	691,000	[1]	2,496,000	[1]	2,341,000	[1]
Loans receivable, other information [Abstract]
Amount of total loan portfolio to businesses and individuals in Oklahoma	5,300,000,000
Percentage of total loan portfolio to businesses and individuals in Oklahoma (in hundredths)	46.00%
Amount of total loan portfolio to businesses and individuals in Texas	3,500,000,000
Percentage of total loan portfolio to businesses and individuals in Texas (in hundredths)	30.00%
Amount of loan portfolio to businesses in Oklahoma							3,100,000,000
Percentage of loan portfolio to businesses in Oklahoma (in hundredths)							44.00%
Amount of loan portfolio to businesses in Texas							2,400,000,000
Percentage of loan portfolio to businesses in Texas (in hundredths)							34.00%
Percentage of energy loans in loan portfolio										20.00%
Amount of loans to energy producers										2,000,000,000
Percentage of committed energy production loans secured by oil										55.00%
Percentage of committed energy production loans secured by natural gas										45.00%
Amount Of loans with individual balances less than $10 million											1,000,000,000
Maximum loan amount for certain individual loans in category											10,000,000
Percentage of loan portfolio secured by property in Texas (in hundredths)												32.00%
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)												30.00%
Minimum FICO required for jumbo loan approval																		720
Maximum debt-to-income ratio on jumbo loans (in hundredths)																		38.00%
Minimum loan-to-value ratio on jumbo loans (in hundredths)																		60.00%
Maximum loan-to-value ratio on jumbo loans (in hundredths)																		100.00%
Minimum period for fixed rate on variable rate jumbo loans (in years)																		3Y
Maximum period for fixed rate on variable rate jumbo loans (in years)																		10Y
Amount of loans guaranteed by US government and previously sold into GNMA mortgage pools																			168,000,000
Percentage of home equity portfolio comprised of junior lien loans																				39.00%
Percentage of home equity portfolio comprised of first lien loans																				61.00%
Percentage of junior lien home equity loans that are amortizing term loans																				79.00%
Percentage of junior lien home equity loans that are revolving lines of credit																				21.00%
Home equity loans, description																				Home equity loans generally require a minimum FICO score of 700 and a maximum DTI of 40%.
Home equity loans, maximum																				400,000
Credit Commitments [Abstract]
Outstanding commitments to extend credit	6,100,000,000
Outstanding standby letters of credit	449,000,000
Outstanding commercial letters of credit	$ 8,000,000

[1] Excludes residential mortgage loans guaranteed by agencies of the U.S. government