Loans and Allowances for Credit Losses, By Aging Category (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing receivable, recorded investment, aging [Abstract]
Current	$ 13,933,715	$ 12,509,986
Past due 30 to 89 days	41,437	38,099
Past due 90 days or more	152,114	143,030
Nonaccrual	80,771	101,149
Total	14,208,037	12,792,264
Commercial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	9,078,724	7,922,000
Past due 30 to 89 days	3,419	4,112
Past due 90 days or more	0	349
Nonaccrual	13,527	16,760
Total	9,095,670	7,943,221
Energy [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,857,082	2,347,267
Past due 30 to 89 days	1,930	2,483
Past due 90 days or more	0	150
Nonaccrual	1,416	1,860
Total	2,860,428	2,351,760
Services [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,511,892	2,276,036
Past due 30 to 89 days	1,136	1,210
Past due 90 days or more	0	42
Nonaccrual	5,201	4,922
Total	2,518,229	2,282,210
Wholesale/retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,309,167	1,193,905
Past due 30 to 89 days	0	338
Past due 90 days or more	0	152
Nonaccrual	4,149	6,969
Total	1,313,316	1,201,364
Manufacturing [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	532,144	391,159
Past due 30 to 89 days	0	0
Past due 90 days or more	0	0
Nonaccrual	450	592
Total	532,594	391,751
Healthcare [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,453,409	1,272,660
Past due 30 to 89 days	180	0
Past due 90 days or more	0	0
Nonaccrual	1,380	1,586
Total	1,454,969	1,274,246
Other commercial and industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	415,030	440,973
Past due 30 to 89 days	173	81
Past due 90 days or more	0	5
Nonaccrual	931	831
Total	416,134	441,890
Commercial Real Estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,704,373	2,370,684
Past due 30 to 89 days	5,220	2,788
Past due 90 days or more	0	1,031
Nonaccrual	18,557	40,850
Total	2,728,150	2,415,353
Residential construction and land development [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	133,642	188,434
Past due 30 to 89 days	4,650	428
Past due 90 days or more	0	19
Nonaccrual	5,299	17,377
Total	143,591	206,258
Retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	662,963	580,926
Past due 30 to 89 days	0	264
Past due 90 days or more	0	0
Nonaccrual	3,926	4,857
Total	666,889	586,047
Office [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	412,124	404,505
Past due 30 to 89 days	0	603
Past due 90 days or more	0	0
Nonaccrual	3,420	6,391
Total	415,544	411,499
Multifamily [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	704,298	576,495
Past due 30 to 89 days	0	0
Past due 90 days or more	0	0
Nonaccrual	0	7
Total	704,298	576,502
Industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	428,817	243,625
Past due 30 to 89 days	0	0
Past due 90 days or more	0	0
Nonaccrual	0	252
Total	428,817	243,877
Other commercial real estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	362,529	376,699
Past due 30 to 89 days	570	1,493
Past due 90 days or more	0	1,012
Nonaccrual	5,912	11,966
Total	369,011	391,170
Residential Mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,717,028	1,837,885
Past due 30 to 89 days	32,251	30,172
Past due 90 days or more	152,112	141,649
Nonaccrual	48,121	42,320
Total	1,949,512	2,052,026
Permanent mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	929,090	1,018,670
Past due 30 to 89 days	5,970	9,795
Past due 90 days or more	46	0
Nonaccrual	34,845	34,279
Total	969,951	1,062,744
Permanent mortgages guaranteed by U.S. government agencies [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	26,691	21,916
Past due 30 to 89 days	23,558	17,290
Past due 90 days or more	151,989	141,615
Nonaccrual	3,712	777
Total	205,950	181,598
Home equity
Financing receivable, recorded investment, aging [Abstract]
Current	761,247	797,299
Past due 30 to 89 days	2,723	3,087
Past due 90 days or more	77	34
Nonaccrual	9,564	7,264
Total	773,611	807,684
Consumer [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	433,590	379,417
Past due 30 to 89 days	547	1,027
Past due 90 days or more	2	1
Nonaccrual	566	1,219
Total	$ 434,705	$ 381,664

Financing receivables that are less than 90 days past due but more than 29 days past due.

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Financing receivables that are current.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

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Financing receivables that are equal to or greater than 90 days past due.

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Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

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