Loans and Allowances for Credit Losses Part 1 (Details) (USD $)	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	$ 6,926,021,000		$ 6,050,429,000
Loans receivables with variable rate of interest	5,251,025,000		5,018,028,000
Loan receivable non-accrual	134,410,000		201,286,000
Total	12,311,456,000		11,269,743,000
Accruing loans past due (90 days)	3,925,000	[1]	2,496,000	[1]
Loans Receivable, Impaired, Foregone Interest on Nonaccrual Loans	8,587,000		11,726,000
Loans receivable, other information [Abstract]
Amount of total loan portfolio to businesses and individuals in Oklahoma	5,400,000,000		5,100,000,000
Percentage of total loan portfolio to businesses and individuals in Oklahoma (in hundredths)	44.00%		45.00%
Amount of total loan portfolio to businesses and individuals in Texas	3,900,000,000		3,500,000,000
Percentage of total loan portfolio to businesses and individuals in Texas (in hundredths)	32.00%		31.00%
Revolving Period for Home Equity Loans	5 years
Amortization Period Following Revolving Period for Home Equity Loans	15 years
Credit Commitments [Abstract]
Outstanding commitments to extend credit	6,600,000,000
Outstanding standby letters of credit	466,000,000
Outstanding commercial letters of credit	7,000,000
Commercial Portfolio Segment [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	4,158,548,000		3,261,344,000
Loans receivables with variable rate of interest	3,458,897,000		3,224,915,000
Loan receivable non-accrual	24,467,000		68,811,000
Total	7,641,912,000		6,555,070,000
Loans receivable, other information [Abstract]
Amount of loan portfolio to businesses in Oklahoma	3,100,000,000		2,800,000,000
Percentage of loan portfolio to businesses in Oklahoma (in hundredths)	40.00%		43.00%
Amount of loan portfolio to businesses in Texas	2,700,000,000		2,200,000,000
Percentage of loan portfolio to businesses in Texas (in hundredths)	36.00%		34.00%
Commercial Portfolio Segment [Member] | Energy [Member]
Loans receivables disclosure [Abstract]
Total	2,500,000,000		2,000,000,000
Loans receivable, other information [Abstract]
Percentage of energy loans in loan portfolio	20.00%
Amount of loans to energy producers	2,200,000,000
Percentage of committed energy production loans secured by oil	55.00%
Percentage of committed energy production loans secured by natural gas	45.00%
Commercial Portfolio Segment [Member] | Services [Member]
Loans receivables disclosure [Abstract]
Total	2,200,000,000		1,800,000,000
Loans receivable, other information [Abstract]
Amount Of loans with individual balances less than $10 million	1,200,000,000		993,000,000
Maximum loan amount for certain individual loans in category	10,000,000		10,000,000
Commercial Real Estate Portfolio Segment [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	845,023,000		896,820,000
Loans receivables with variable rate of interest	1,323,350,000		1,295,290,000
Loan receivable non-accrual	60,626,000		99,193,000
Total	2,228,999,000		2,291,303,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)	35.00%		36.00%
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	26.00%		26.00%
Residential Portfolio Segment [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	1,747,038,000		1,646,554,000
Loans receivables with variable rate of interest	251,394,000		298,206,000
Loan receivable non-accrual	46,608,000		29,767,000
Total	2,045,040,000		1,974,527,000
Residential Portfolio Segment [Member] | Permanent mortgage [Member]
Loans receivable, other information [Abstract]
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%
Period For Fixed Rate On Variable Rate Jumbo Loans Minimum	3 years
Period For Fixed Rate On Variable Rate Jumbo Loans Maximum	10 years
Residential Portfolio Segment [Member] | Permanent mortgages guaranteed by U.S. government agencies [Member]
Loans receivables disclosure [Abstract]
Total	160,000,000		185,000,000
Residential Portfolio Segment [Member] | Home equity [Member]
Loans receivables disclosure [Abstract]
Total	761,000,000		632,000,000
Loans receivable, other information [Abstract]
Percentage of home equity portfolio comprised of first lien loans	68.00%		66.00%
Percentage of home equity portfolio comprised of junior lien loans	32.00%		34.00%
Percentage of junior lien home equity loans that are amortizing term loans	78.00%		78.00%
Percentage of junior lien home equity loans that are revolving lines of credit	22.00%		22.00%
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
Consumer Portfolio Segment [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	175,412,000		245,711,000
Loans receivables with variable rate of interest	217,384,000		199,617,000
Loan receivable non-accrual	2,709,000		3,515,000
Total	$ 395,505,000		$ 448,843,000

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