CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets [Abstract]
Cash and noninterest-bearing due from banks	$ 189,251	$ 203,296
Restricted Cash, Current	162,834	223,788
Interest-bearing due from banks	2,780,137	3,522,224
Federal funds sold and other	55,186	12,141
Cash and cash equivalents	3,187,408	3,961,449
Securities Purchased under Agreements to Resell	450,000	0
Available-for-sale Securities	3,677,019	3,586,681
Securities held-to-maturity (fair value of $1.0 billion and $1.1 billion, net of allowance for credit losses of $198 and $191 at March 31, 2021 and Dec. 31, 2020, respectively)	1,014,345	1,028,359
Consumer loans held-for-sale	85,769	87,821
Commercial loans held-for-sale	12,541	31,200
Loans and Leases Receivable, Net of Deferred Income	23,086,701	22,424,501
Less allowance for credit losses	(280,881)	(285,050)
Loans, net	22,805,820	22,139,451
Premises and equipment, net	289,515	290,001
Equity method investment	327,512	308,556
Accrued interest receivable	98,477	104,078
Goodwill	1,819,811	1,819,811
Core deposits and other intangible assets	40,130	42,336
Other real estate owned	10,651	12,360
Other assets	1,480,707	1,520,757
Total assets	35,299,705	34,932,860
Deposits:
Noninterest-bearing	8,103,943	7,392,325
Interest-bearing	5,814,689	5,689,095
Savings and money market accounts	11,361,620	11,099,523
Time	3,012,688	3,524,632
Total deposits	28,292,940	27,705,575
Securities sold under agreements to repurchase	172,117	128,164
Federal Home Loan Bank advances	888,115	1,087,927
Subordinated debt and other borrowings	671,002	670,575
Accrued interest payable	15,359	24,934
Other liabilities	300,648	411,074
Total liabilities	30,340,181	30,028,249
Shareholders' equity:
Preferred stock, no par value, 10.0 million shares authorized; 225,000 shares non-cumulative perpetual preferred stock, Series B, liquidation preference $225.0 million, issued and outstanding at March 31, 2021 and Dec. 31, 2020, respectively	217,126	217,126
Common stock, par value $1.00; 180.0 million shares authorized; 76.1 million and 75.9 million shares issued and outstanding at March 31, 2021 and Dec. 31, 2020, respectively	76,088	75,850
Additional paid-in capital	3,027,311	3,028,063
Retained earnings	1,515,451	1,407,723
Accumulated other comprehensive income, net of taxes	123,548	175,849
Total shareholders' equity	4,959,524	4,904,611
Liabilities and Equity	$ 35,299,705	$ 34,932,860