Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 16,316,211	$ 14,409,398	$ 14,052,059
Covered loans	168,609	226,709	254,605
Total loans	$ 16,484,820	$ 14,636,107	$ 14,306,664
Total loans, net of unearned income, excluding covered loans, percentage	99.00%	98.00%	98.00%
Covered loans, percentage	1.00%	2.00%	2.00%
Total loans, percentage	100.00%	100.00%	100.00%
Commercial
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 4,400,185	$ 3,924,394	$ 3,689,671
Total loans, net of unearned income, excluding covered loans, percentage	27.00%	26.00%	26.00%
Commercial real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 5,307,566	$ 4,505,753	$ 4,510,375
Total loans, net of unearned income, excluding covered loans, percentage	32.00%	31.00%	31.00%
Home equity
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 797,465	$ 716,293	$ 720,058
Total loans, net of unearned income, excluding covered loans, percentage	5.00%	5.00%	5.00%
Residential real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 571,743	$ 483,542	$ 470,319
Total loans, net of unearned income, excluding covered loans, percentage	3.00%	3.00%	3.00%
Consumer and other
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 131,902	$ 151,012	$ 149,339
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	$ 2,407,075	$ 2,350,833	$ 2,377,892
Total loans, net of unearned income, excluding covered loans, percentage	15.00%	16.00%	17.00%
Life insurance \| Premium finance receivables
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 2,700,275	$ 2,277,571	$ 2,134,405
Total loans, net of unearned income, excluding covered loans, percentage	16.00%	16.00%	15.00%

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=28367877&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=49124121&loc=d3e5074-111524

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