Loans and Allowances for Credit Losses, By Aging Category (Details) (USD $)	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Financing receivable, recorded investment, aging [Abstract]
Current	$ 13,403,666,000	$ 12,509,986,000	$ 12,079,201,000
Past due 30 to 89 days	47,637,000	38,099,000	34,089,000
Past due 90 days or more	135,885,000	143,030,000	123,906,000
Nonaccrual	96,551,000	101,149,000	112,904,000
Total	13,683,739,000	12,792,264,000	12,350,100,000
Commercial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	8,552,998,000	7,922,000,000	7,547,586,000
Past due 30 to 89 days	2,631,000	4,112,000	3,882,000
Past due 90 days or more	5,000	349,000	85,000
Nonaccrual	16,404,000	16,760,000	19,522,000
Total	8,572,038,000	7,943,221,000	7,571,075,000
Energy [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,549,441,000	2,347,267,000	2,308,639,000
Past due 30 to 89 days	750,000	2,483,000	1,399,000
Past due 90 days or more	0	150,000	0
Nonaccrual	1,508,000	1,860,000	1,953,000
Total	2,551,699,000	2,351,760,000	2,311,991,000
Services [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,483,416,000	2,276,036,000	2,140,835,000
Past due 30 to 89 days	812,000	1,210,000	704,000
Past due 90 days or more	5,000	42,000	85,000
Nonaccrual	3,584,000	4,922,000	6,927,000
Total	2,487,817,000	2,282,210,000	2,148,551,000
Wholesale/retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,267,206,000	1,193,905,000	1,173,628,000
Past due 30 to 89 days	533,000	338,000	955,000
Past due 90 days or more	0	152,000	0
Nonaccrual	5,502,000	6,969,000	7,223,000
Total	1,273,241,000	1,201,364,000	1,181,806,000
Manufacturing [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	475,595,000	391,159,000	381,048,000
Past due 30 to 89 days	466,000	0	569,000
Past due 90 days or more	0	0	0
Nonaccrual	3,482,000	592,000	843,000
Total	479,543,000	391,751,000	382,460,000
Healthcare [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,380,982,000	1,272,660,000	1,158,340,000
Past due 30 to 89 days	0	0	139,000
Past due 90 days or more	0	0	0
Nonaccrual	1,417,000	1,586,000	1,733,000
Total	1,382,399,000	1,274,246,000	1,160,212,000
Other commercial and industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	396,358,000	440,973,000	385,096,000
Past due 30 to 89 days	70,000	81,000	116,000
Past due 90 days or more	0	5,000	0
Nonaccrual	911,000	831,000	843,000
Total	397,339,000	441,890,000	386,055,000
Commercial Real Estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	2,682,921,000	2,370,684,000	2,295,456,000
Past due 30 to 89 days	10,618,000	2,788,000	1,271,000
Past due 90 days or more	0	1,031,000	0
Nonaccrual	30,660,000	40,850,000	52,502,000
Total	2,724,199,000	2,415,353,000	2,349,229,000
Residential construction and land development [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	152,399,000	188,434,000	195,672,000
Past due 30 to 89 days	8,195,000	428,000	0
Past due 90 days or more	0	19,000	0
Nonaccrual	14,634,000	17,377,000	20,784,000
Total	175,228,000	206,258,000	216,456,000
Retail [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	606,383,000	580,926,000	548,810,000
Past due 30 to 89 days	873,000	264,000	194,000
Past due 90 days or more	0	0	0
Nonaccrual	4,009,000	4,857,000	7,914,000
Total	611,265,000	586,047,000	556,918,000
Office [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	434,160,000	404,505,000	415,205,000
Past due 30 to 89 days	1,250,000	603,000	0
Past due 90 days or more	0	0	0
Nonaccrual	3,499,000	6,391,000	6,838,000
Total	438,909,000	411,499,000	422,043,000
Multifamily [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	739,757,000	576,495,000	516,104,000
Past due 30 to 89 days	0	0	0
Past due 90 days or more	0	0	0
Nonaccrual	0	7,000	4,350,000
Total	739,757,000	576,502,000	520,454,000
Industrial [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	371,426,000	243,625,000	244,415,000
Past due 30 to 89 days	0	0	607,000
Past due 90 days or more	0	0	0
Nonaccrual	0	252,000	0
Total	371,426,000	243,877,000	245,022,000
Other commercial real estate [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	378,796,000	376,699,000	375,250,000
Past due 30 to 89 days	300,000	1,493,000	470,000
Past due 90 days or more	0	1,012,000	0
Nonaccrual	8,518,000	11,966,000	12,616,000
Total	387,614,000	391,170,000	388,336,000
Residential Mortgage [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	1,761,284,000	1,837,885,000	1,844,555,000
Past due 30 to 89 days	33,592,000	30,172,000	27,208,000
Past due 90 days or more	135,880,000	141,649,000	123,746,000
Nonaccrual	48,907,000	42,320,000	39,256,000
Total	1,979,663,000	2,052,026,000	2,034,765,000
Permanent mortage [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	947,791,000	1,018,670,000	1,040,616,000
Past due 30 to 89 days	8,179,000	9,795,000	6,248,000
Past due 90 days or more	0	0	0
Nonaccrual	35,137,000	34,279,000	31,797,000
Total	991,107,000	1,062,744,000	1,078,661,000
Permanent mortgages guaranteed by US govenment agencies [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	35,318,000	21,916,000	20,985,000
Past due 30 to 89 days	23,475,000	17,290,000	18,639,000
Past due 90 days or more	135,860,000	141,615,000	123,718,000
Nonaccrual	3,835,000	777,000	577,000
Total	198,488,000	181,598,000	163,919,000
Home equity {Member]
Financing receivable, recorded investment, aging [Abstract]
Current	778,175,000	797,299,000	782,954,000
Past due 30 to 89 days	1,938,000	3,087,000	2,321,000
Past due 90 days or more	20,000	34,000	28,000
Nonaccrual	9,935,000	7,264,000	6,882,000
Total	790,068,000	807,684,000	792,185,000
Consumer [Member]
Financing receivable, recorded investment, aging [Abstract]
Current	406,463,000	379,417,000	391,604,000
Past due 30 to 89 days	796,000	1,027,000	1,728,000
Past due 90 days or more	0	1,000	75,000
Nonaccrual	580,000	1,219,000	1,624,000
Total	$ 407,839,000	$ 381,664,000	$ 395,031,000