Loans and Allowances for Credit Losses Part 1 (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	$ 4,327,637,000		$ 5,657,343,000
Loans receivables with variable rate of interest	8,363,478,000		6,519,703,000
Loan receivable non-accrual	101,149,000		134,410,000
Total	12,792,264,000		12,311,456,000
Accruing loans past due (90 days)	1,415,000	[1]	3,925,000	[1]
Loans Receivable, Impaired, Foregone Interest on Nonaccrual Loans	5,361,000		8,587,000
Loans receivable, other information [Abstract]
Amount of total loan portfolio to businesses and individuals in Texas	4,300,000,000		4,000,000,000
Percentage of total loan portfolio to businesses and individuals in Texas (in hundredths)	34.00%		32.00%
Amount of total loan portfolio to businesses and individuals in Oklahoma	3,300,000,000		3,300,000,000
Percentage of total loan portfolio to businesses and individuals in Oklahoma (in hundredths)	26.00%		27.00%
Credit Commitments [Abstract]
Outstanding commitments to extend credit	7,100,000,000
Outstanding standby letters of credit	444,000,000
Outstanding commercial letters of credit	13,000,000
Commercial [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	1,637,620,000		2,955,779,000
Loans receivables with variable rate of interest	6,288,841,000		4,661,666,000
Loan receivable non-accrual	16,760,000		24,467,000
Total	7,943,221,000		7,641,912,000
Loans receivable, other information [Abstract]
Amount of loan portfolio to businesses in Texas	2,800,000,000		2,600,000,000
Percentage of loan portfolio to businesses in Texas (in hundredths)	36.00%		34.00%
Amount of loan portfolio to businesses in Oklahoma	1,900,000,000		1,900,000,000
Percentage of loan portfolio to businesses in Oklahoma (in hundredths)	23.00%		25.00%
Energy [Member]
Loans receivables disclosure [Abstract]
Total	2,351,760,000		2,460,659,000
Loans receivable, other information [Abstract]
Percentage of energy loans in loan portfolio	18.00%
Amount of loans to energy producers	2,000,000,000
Percentage of committed energy production loans secured by oil	59.00%
Percentage of committed energy production loans secured by natural gas	41.00%
Services [Member]
Loans receivables disclosure [Abstract]
Total	2,282,210,000		2,164,186,000
Loans receivable, other information [Abstract]
Amount of loans with individual balances less than $10 million	1,100,000,000		993,000,000
Maximum loan amount for certain individual loans in category	10,000,000		10,000,000
Commercial Real Estate [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	770,908,000		779,114,000
Loans receivables with variable rate of interest	1,603,595,000		1,389,259,000
Loan receivable non-accrual	40,850,000		60,626,000
Total	2,415,353,000		2,228,999,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)	31.00%		32.00%
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	19.00%		19.00%
Percentage of loan portfolio secured by property in New Mexico (in hundredths)	11.00%		13.00%
Residential Mortgage [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	1,783,615,000		1,747,038,000
Loans receivables with variable rate of interest	226,092,000		251,394,000
Loan receivable non-accrual	42,319,000		46,608,000
Total	2,052,026,000		2,045,040,000
Loans receivable, other information [Abstract]
Percentage of loan portfolio secured by property in Texas (in hundredths)	27.00%		34.00%
Percentage of loan portfolio secured by property in Oklahoma (in hundredths)	38.00%		23.00%
Percentage of loan portfolio secured by property in New Mexico (in hundredths)	12.00%		17.00%
Percentage of loan portfolio secured by property in Colorado	10.00%		11.00%
Permanent Mortgage [Member]
Loans receivables disclosure [Abstract]
Total	1,062,744,000		1,123,965,000
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%
Minimum period for fixed rate on variable rate jumbo loans (in years)	3 years
Maximum period for fixed rate on variable rate jumbo loans (in years)	10 years
Permanent mortgages guaranteed by U.S. government agencies [Member]
Loans receivables disclosure [Abstract]
Total	181,598,000		160,444,000
Loans receivable, other information [Abstract]
Amount of loan portfolio guaranteed by US government previously sold into GNMA mortgage pools	182,000,000		160,000,000
Home equity
Loans receivables disclosure [Abstract]
Total	807,684,000		760,631,000
Loans receivable, other information [Abstract]
Percentage of home equity portfolio comprised of first lien loans	70.00%		68.00%
Percentage of home equity portfolio comprised of junior lien loans	30.00%		32.00%
Percentage of junior lien home equity loans that are amortizing term loans	74.00%		78.00%
Percentage of junior lien home equity loans that are revolving lines of credit	26.00%		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
Home equity loans, revolving period	5 years
Home equity loans, amortization period following revolving period	15 years
Home equity loans, discretionary additional revolving period	5 years
Consumer [Member]
Loans receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	135,494,000		175,412,000
Loans receivables with variable rate of interest	244,950,000		217,384,000
Loan receivable non-accrual	1,220,000		2,709,000
Total	$ 381,664,000		$ 395,505,000

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