Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets [Abstract]
Cash and due from banks	$ 718,297	$ 741,749
Interest-bearing cash and cash equivalents	564,404	401,675
Trading securities	2,140,326	1,956,923
Investment securities	331,466	355,187
Available for sale securities	9,025,198	8,857,120
Fair value option securities	707,994	283,235
Restricted equity securities	376,429	344,447
Residential mortgage loans held for sale	160,157	149,221
Loans	21,758,980	21,656,730
Allowance for loan losses	(205,340)	(207,457)
Loans, net of allowance	21,553,640	21,449,273
Premises and equipment, net	468,293	330,033
Receivables	224,887	204,960
Goodwill	1,048,091	1,049,263
Intangible assets, net	129,482	134,849
Mortgage servicing rights	238,193	259,254
Real estate and other repossessed assets, net of allowance	17,139	17,487
Derivative contracts, net	359,223	320,929
Cash surrender value of bank-owned life insurance	384,174	381,608
Receivable on unsettled securities sales	966,455	336,400
Other assets	469,114	446,891
Total assets	39,882,962	38,020,504
Deposits [Abstract]
Noninterest-bearing demand deposits	10,096,552	10,414,592
Interest-bearing deposits: [Abstract]
Transaction	12,476,977	12,206,576
Savings	559,884	529,215
Time	2,198,389	2,113,380
Total deposits	25,331,802	25,263,763
Funds purchased and repurchase agreements	1,439,673	1,018,411
Other borrowings	7,341,093	6,124,390
Subordinated debentures	275,880	275,913
Accrued interest, taxes and expense	173,434	192,826
Derivative contracts, net	299,698	362,306
Due on unsettled securities purchases	186,401	156,370
Other liabilities	303,272	183,480
Total liabilities	35,351,253	33,577,459
Shareholders' equity: [Abstract]
Common stock	5	5
Capital surplus	1,340,323	1,334,030
Retained earnings	3,447,076	3,369,654
Treasury stock	(261,000)	(198,995)
Accumulated other comprehensive loss	(3,531)	(72,585)
Total shareholders’ equity	4,522,873	4,432,109
Non-controlling interests	8,836	10,936
Total equity	4,531,709	4,443,045
Total liabilities and equity	$ 39,882,962	$ 38,020,504