Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 19,101,261	$ 17,118,117	$ 16,316,211
Covered loans	95,940	148,673	168,609
Total loans	$ 19,197,201	$ 17,266,790	$ 16,484,820
Total loans, net of unearned income, excluding covered loans, percentage	100.00%	99.00%	99.00%
Covered loans, percentage	0.00%	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	$ 5,951,544	$ 4,713,909	$ 4,400,185
Total loans, net of unearned income, excluding covered loans, percentage	31.00%	27.00%	27.00%
Commercial real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 5,908,684	$ 5,529,289	$ 5,307,566
Total loans, net of unearned income, excluding covered loans, percentage	31.00%	32.00%	32.00%
Home equity
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 742,868	$ 784,675	$ 797,465
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	$ 663,598	$ 607,451	$ 571,743
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	$ 120,975	$ 146,376	$ 131,902
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	$ 2,430,233	$ 2,374,921	$ 2,407,075
Total loans, net of unearned income, excluding covered loans, percentage	13.00%	14.00%	15.00%
Life insurance \| Premium finance receivables
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 3,283,359	$ 2,961,496	$ 2,700,275
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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