Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 20,743,332	$ 19,703,172	$ 18,174,655
Covered loans	50,119	58,145	105,248
Total loans	$ 20,793,451	$ 19,761,317	$ 18,279,903
Total loans, net of unearned income, excluding covered loans, percentage	100.00%	100.00%	99.00%
Covered loans, percentage	0.00%	0.00%	1.00%
Total loans, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 6,406,289	$ 6,005,422	$ 5,144,533
Total loans, net of unearned income, excluding covered loans, percentage	31.00%	30.00%	28.00%
Commercial real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 6,402,494	$ 6,196,087	$ 5,848,334
Total loans, net of unearned income, excluding covered loans, percentage	31.00%	31.00%	31.00%
Home equity
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 689,483	$ 725,793	$ 760,904
Total loans, net of unearned income, excluding covered loans, percentage	3.00%	4.00%	4.00%
Residential real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 762,810	$ 705,221	$ 653,664
Total loans, net of unearned income, excluding covered loans, percentage	3.00%	4.00%	4.00%
Consumer and other
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 114,827	$ 122,041	$ 127,378
Total loans, net of unearned income, excluding covered loans, percentage	1.00%	1.00%	1.00%
Commercial insurance loans \| Premium finance receivables
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 2,648,386	$ 2,478,581	$ 2,478,280
Total loans, net of unearned income, excluding covered loans, percentage	13.00%	12.00%	14.00%
Life insurance \| Premium finance receivables
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 3,719,043	$ 3,470,027	$ 3,161,562
Total loans, net of unearned income, excluding covered loans, percentage	18.00%	18.00%	17.00%

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5074-111524

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