Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 18,174,655	$ 17,118,117	$ 15,513,650
Covered loans	105,248	148,673	193,410
Total loans	$ 18,279,903	$ 17,266,790	$ 15,707,060
Total loans, net of unearned income, excluding covered loans, percentage	99.00%	99.00%	99.00%
Covered loans, percentage	1.00%	1.00%	1.00%
Total loans, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 5,144,533	$ 4,713,909	$ 4,330,344
Total loans, net of unearned income, excluding covered loans, percentage	28.00%	27.00%	27.00%
Commercial real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 5,848,334	$ 5,529,289	$ 4,850,590
Total loans, net of unearned income, excluding covered loans, percentage	31.00%	32.00%	31.00%
Home equity
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 760,904	$ 784,675	$ 712,350
Total loans, net of unearned income, excluding covered loans, percentage	4.00%	5.00%	5.00%
Residential real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 653,664	$ 607,451	$ 503,015
Total loans, net of unearned income, excluding covered loans, percentage	4.00%	3.00%	3.00%
Consumer and other
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 127,378	$ 146,376	$ 119,468
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	$ 2,478,280	$ 2,374,921	$ 2,460,408
Total loans, net of unearned income, excluding covered loans, percentage	14.00%	14.00%	16.00%
Life insurance \| Premium finance receivables
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 3,161,562	$ 2,961,496	$ 2,537,475
Total loans, net of unearned income, excluding covered loans, percentage	17.00%	17.00%	16.00%

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=65884687&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=66008989&loc=d3e5074-111524

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