Loans and Allowance for Credit Losses Part 1 (Details) (USD $)																				9 Months Ended
	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011		Sep. 30, 2012 Commercial Portfolio Segment [Member]	Dec. 31, 2011 Commercial Portfolio Segment [Member]	Sep. 30, 2011 Commercial Portfolio Segment [Member]	Sep. 30, 2012 Commercial Portfolio Segment [Member] Energy [Member]	Sep. 30, 2012 Commercial Portfolio Segment [Member] Services [Member]	Sep. 30, 2012 Commercial Real Estate Portfolio Segment [Member]	Dec. 31, 2011 Commercial Real Estate Portfolio Segment [Member]	Sep. 30, 2011 Commercial Real Estate Portfolio Segment [Member]	Sep. 30, 2012 Residential Portfolio Segment [Member]	Dec. 31, 2011 Residential Portfolio Segment [Member]	Sep. 30, 2011 Residential Portfolio Segment [Member]	Sep. 30, 2012 Residential Portfolio Segment [Member] Permanent mortgage [Member]	Sep. 30, 2012 Residential Portfolio Segment [Member] Permanent mortgages guaranteed by U.S. government agencies [Member]	Sep. 30, 2012 Residential Portfolio Segment [Member] Home equity [Member]	Sep. 30, 2012 Consumer Portfolio Segment [Member]	Dec. 31, 2011 Consumer Portfolio Segment [Member]	Sep. 30, 2011 Consumer Portfolio Segment [Member]
Loan receivables disclosure [Abstract]
Loans receivables with fixed rate of interest	$ 6,611,080,000		$ 6,050,429,000		$ 5,784,709,000		$ 3,829,409,000	$ 3,261,344,000	$ 3,052,708,000			$ 871,211,000	$ 896,820,000	$ 854,800,000	$ 1,728,537,000	$ 1,646,554,000	$ 1,606,799,000				$ 181,923,000	$ 245,711,000	$ 270,402,000
Loans receivables with variable rate of interest	5,089,388,000		5,018,028,000		5,110,385,000		3,422,046,000	3,224,915,000	3,285,158,000			1,218,554,000	1,295,290,000	1,307,985,000	261,176,000	298,206,000	311,371,000				187,612,000	199,617,000	205,871,000
Loan receivable non-accrual	131,899,000		201,286,000		229,475,000		21,762,000	68,811,000	83,736,000			75,761,000	99,193,000	110,048,000	29,267,000	29,767,000	31,731,000				5,109,000	3,515,000	3,960,000
Total	11,832,367,000		11,269,743,000		11,124,569,000		7,273,217,000	6,555,070,000	6,421,602,000	2,300,000,000	1,900,000,000	2,165,526,000	2,291,303,000	2,272,833,000	2,018,980,000	1,974,527,000	1,949,901,000			715,000,000	374,644,000	448,843,000	480,233,000
Accruing loans past due (90 days)	1,181,000	[1]	2,496,000	[1]	1,401,000	[1]
Loans receivable, other information [Abstract]
Amount of total loan portfolio to businesses and individuals in Oklahoma	5,500,000,000
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	3,600,000,000
Percentage of total loan portfolio to businesses and individuals in Texas (in hundredths)	31.00%
Amount of loan portfolio to businesses in Oklahoma							3,100,000,000
Percentage of loan portfolio to businesses in Oklahoma (in hundredths)							43.00%
Amount of loan portfolio to businesses in Texas							2,400,000,000
Percentage of loan portfolio to businesses in Texas (in hundredths)							35.00%
Percentage of energy loans in loan portfolio										21.00%
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%
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)												33.00%
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																			169,000,000
Percentage of home equity portfolio comprised of junior lien loans																				36.00%
Percentage of home equity portfolio comprised of first lien loans																				64.00%
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	6,400,000,000
Outstanding standby letters of credit	448,000,000
Outstanding commercial letters of credit	$ 6,000,000

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