Loans (Summary of Loan Portfolio) (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 17,446,413	$ 17,118,117	$ 14,953,059
Covered loans	138,848	148,673	209,694
Total loans	$ 17,585,261	$ 17,266,790	$ 15,162,753
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	$ 4,890,246	$ 4,713,909	$ 4,211,932
Total loans, net of unearned income, excluding covered loans, percentage	28.00%	27.00%	28.00%
Commercial real estate
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 5,737,959	$ 5,529,289	$ 4,710,486
Total loans, net of unearned income, excluding covered loans, percentage	32.00%	32.00%	31.00%
Home equity
Loans [Line Items]
Loans, net of unearned income, excluding covered loans	$ 774,342	$ 784,675	$ 709,283
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	$ 626,043	$ 607,451	$ 495,925
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	$ 119,902	$ 146,376	$ 130,156
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	$ 2,320,987	$ 2,374,921	$ 2,319,623
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	$ 2,976,934	$ 2,961,496	$ 2,375,654
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=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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