Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Assets [Abstract]
Cash and due from banks	$ 535,916	$ 573,699	$ 489,268
Interest-bearing cash and cash equivalents	2,080,978	2,069,900	1,830,105
Trading securities	546,615	122,404	181,131
Investment securities	546,457	597,836	612,384
Available for sale securities	8,862,283	9,042,733	8,801,089
Fair value option securities	222,409	444,217	427,760
Restricted equity securities	333,391	273,684	263,587
Residential mortgage loans held for sale	447,592	308,439	357,414
Loans	16,464,786	15,941,154	15,367,441
Allowance for loan losses	(245,103)	(225,524)	(204,116)
Loans, net of allowance	16,219,683	15,715,630	15,163,325
Premises and equipment, net	318,196	306,490	294,669
Receivables	650,368	163,480	151,451
Goodwill	382,739	385,461	385,461
Intangible assets, net	41,977	43,909	44,999
Mortgage servicing rights	203,621	218,605	200,049
Real estate and other repossessed assets, net of allowance	31,941	30,731	33,116
Derivative contracts, net	655,078	586,270	726,159
Cash surrender value of bank-owned life insurance	310,211	303,335	300,981
Receivable on unsettled securities sales	19,642	40,193	30,009
Other assets	370,134	249,112	273,948
Total assets	32,779,231	31,476,128	30,566,905
Deposits [Abstract]
Noninterest-bearing demand deposits	8,681,364	8,296,888	8,041,767
Interest-bearing deposits: [Abstract]
Transaction	9,824,160	9,998,954	9,698,849
Savings	420,349	386,252	380,296
Time	2,169,631	2,406,064	2,498,531
Total deposits	21,095,504	21,088,158	20,619,443
Funds purchased	109,031	491,192	62,297
Repurchase agreements	504,573	722,444	555,677
Other borrowings	6,533,443	4,837,879	4,635,150
Subordinated debentures	144,631	226,350	226,314
Accrued interest, taxes and expense	191,276	119,584	158,048
Derivative contracts, net	573,987	581,701	636,115
Due on unsettled securities purchases	677	16,897	98,351
Other liabilities	193,698	124,284	159,348
Total liabilities	29,346,820	28,208,489	27,150,743
Shareholders' equity: [Abstract]
Common stock	4	4	4
Capital surplus	995,680	982,009	973,824
Retained earnings	2,801,931	2,704,121	2,673,292
Treasury stock	(495,031)	(477,165)	(355,670)
Accumulated other comprehensive income	95,727	21,587	85,776
Total shareholders’ equity	3,398,311	3,230,556	3,377,226
Non-controlling interests	34,100	37,083	38,936
Total equity	3,432,411	3,267,639	3,416,162
Total liabilities and equity	$ 32,779,231	$ 31,476,128	$ 30,566,905