Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Assets [Abstract]
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 231,158	$ 190,663
Interest-bearing deposits	25,628	29,461
Securities available-for-sale, at fair value	2,638,037	2,991,091
Investment securities held-to-maturity (fair value of $4,456,350 and $4,125,125)	4,487,392	4,160,658
Federal Home Loan Bank and Federal Reserve Bank stock	151,566	194,646
Loans held for sale (valued under fair value option $20,888 and $60,260)	20,888	67,577
Loans and leases	17,523,858	17,026,588
Allowance for loan and lease losses	(199,994)	(194,320)
Loans and leases, net	17,323,864	16,832,268
Deferred tax assets, net	92,630	84,391
Premises and equipment, net	130,001	137,413
Goodwill	538,373	538,373
Other intangible assets, net	29,611	33,674
Cash surrender value of life insurance policies	531,820	517,852
Accrued interest receivable and other assets	286,677	294,462
Total assets	26,487,645	26,072,529
Liabilities and Equity [Abstract]
Non-interest-bearing	4,191,496	4,021,061
Interest-bearing	16,802,233	15,282,796
Total deposits	20,993,729	19,303,857
Securities sold under agreements to repurchase and other borrowings	643,269	949,526
Federal Home Loan Bank advances	1,677,105	2,842,908
Long-term debt	225,767	225,514
Accrued expenses and other liabilities	245,817	223,712
Total liabilities	23,785,687	23,545,517
Shareholders’ equity:
Common stock, $.01 par value: Authorized - 200,000,000 shares; (Issued 93,651,601 shares)	937	937
Paid-in capital	1,122,164	1,125,937
Retained earnings	1,595,762	1,425,320
Treasury stock, at cost (1,658,526 and 1,899,502 shares)	(70,430)	(70,899)
Accumulated other comprehensive loss, net of tax	(91,531)	(76,993)
Total shareholders' equity	2,701,958	2,527,012
Total liabilities and shareholders' equity	26,487,645	26,072,529
Series F Preferred Stock [Member]
Shareholders’ equity:
Preferred stock, $.01 par value; Authorized - 3,000,000 shares: Series E issued and outstanding (5,060 shares) Series E issued and outstanding (5,060 shares)Series F issued and outstanding(6,000)Series E issued and outstanding (5,060 shares)	145,056	0
Series E Preferred Stock [Member]
Shareholders’ equity:
Preferred stock, $.01 par value; Authorized - 3,000,000 shares: Series E issued and outstanding (5,060 shares) Series E issued and outstanding (5,060 shares)Series F issued and outstanding(6,000)Series E issued and outstanding (5,060 shares)	$ 0	$ 122,710