Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets [Abstract]
Cash and due from banks	$ 723,983	$ 798,757
Interest-bearing cash and cash equivalents	695,213	381,816
Trading securities	5,085,949	4,707,975
Investment securities, net of allowance	226,121	244,843
Available for sale securities	13,410,057	13,050,665
Fair value option securities	72,498	114,982
Restricted equity securities	139,614	171,391
Residential mortgage loans held for sale	284,447	252,316
Loans and Leases Receivable, Gross	22,533,847	23,007,520
Allowance for loan losses	(352,402)	(388,640)
Loans, net of allowance	22,181,445	22,618,880
Premises and equipment, net	555,455	551,308
Receivables	250,852	245,880
Goodwill	1,048,091	1,048,091
Intangible assets, net	110,585	113,436
Mortgage servicing rights	132,915	101,172
Real estate and other repossessed assets, net of allowance	70,911	90,526
Derivative contracts, net	1,289,156	810,688
Cash surrender value of bank-owned life insurance	401,320	398,758
Receivable on unsettled securities sales	67,759	62,386
Other assets	696,142	907,218
Total assets	47,442,513	46,671,088
Deposits [Abstract]
Noninterest-bearing demand deposits	13,103,170	12,266,338
Interest-bearing deposits: [Abstract]
Transaction	21,890,874	21,158,422
Savings	854,226	751,992
Time	2,004,356	1,967,128
Total deposits	37,852,626	36,143,880
Funds purchased and repurchase agreements	795,161	1,662,386
Other borrowings	1,708,517	1,882,970
Subordinated debentures	276,024	276,005
Accrued interest, taxes and expense	290,328	323,667
Derivative contracts, net	719,556	405,779
Due on unsettled securities purchases	106,835	257,627
Other liabilities	431,122	427,213
Total liabilities	42,180,169	41,379,527
Shareholders' equity: [Abstract]
Common stock	5	5
Capital surplus	1,371,735	1,368,062
Retained earnings	4,083,543	3,973,675
Treasury stock	(437,230)	(411,344)
Accumulated other comprehensive gain	221,409	335,868
Total shareholders’ equity	5,239,462	5,266,266
Non-controlling interests	22,882	25,295
Total equity	5,262,344	5,291,561
Total liabilities and equity	$ 47,442,513	$ 46,671,088