Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets [Abstract]
Cash and due from banks	$ 181,524	$ 185,341
Interest-bearing deposits	60,276	72,554
Investment securities available-for-sale, at fair value	3,304,217	2,925,833
Investment securities held-to-maturity, net	5,723,434	5,293,918
Allowance for credit losses on investment securities held-to-maturity	(306)	0
Investment securities held-to-maturity, net	5,723,128	5,293,918
Federal Home Loan Bank and Federal Reserve Bank stock	89,611	149,046
Loans held for sale (valued under fair value option $29,018 and $35,750)	29,018	36,053
Loans and leases	21,852,023	20,036,986
Allowance for credit losses on loans and leases	(369,811)	(209,096)
Loans and leases, net	21,482,212	19,827,890
Deferred tax assets, net	76,695	61,975
Premises and equipment, net	250,535	270,413
Goodwill	538,373	538,373
Other intangible assets, net	23,529	21,917
Cash surrender value of life insurance policies	561,021	550,651
Accrued interest receivable and other assets	674,304	455,380
Total assets	32,994,443	30,389,344
Liabilities and Equity [Abstract]
Non-interest-bearing	6,136,814	4,446,463
Interest-bearing	20,783,739	18,878,283
Total deposits	26,920,553	23,324,746
Securities sold under agreements to repurchase and other borrowings	1,301,822	1,040,431
Federal Home Loan Bank advances	433,243	1,948,476
Long-term debt	568,846	540,364
Operating lease liabilities	165,211	174,396
Accrued expenses and other liabilities	385,078	153,161
Total liabilities	29,774,753	27,181,574
Stockholders' Equity Attributable to Parent [Abstract]
Preferred stock	145,037	145,037
Common stock	937	937
Paid-in capital	1,106,473	1,113,250
Retained earnings	2,055,620	2,061,352
Treasury stock, at cost (3,482,493 and 1,659,749 shares)	(140,414)	(76,734)
Accumulated other comprehensive income (loss), net of tax	52,037	(36,072)
Total shareholders' equity	3,219,690	3,207,770
Total liabilities and shareholders' equity	$ 32,994,443	$ 30,389,344