Investment Securities (Amortized Cost and Fair Values of Investment Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	$ 2,350,338	$ 2,520,824
Available-for-Sale, Gross Unrealized Gains	68,259	76,087
Available-for-Sale, Gross Unrealized Losses	17,971	19,010
Total available-for-sale securities, Fair Value	2,400,626	2,577,901
U.S. Government Agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	113,328	113,367
Available-for-Sale, Gross Unrealized Gains	808	1,041
Available-for-Sale, Gross Unrealized Losses	0	0
Total available-for-sale securities, Fair Value	114,136	114,408
Obligations Of States And Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	399,419	403,487
Available-for-Sale, Gross Unrealized Gains	27,604	32,585
Available-for-Sale, Gross Unrealized Losses	579	295
Total available-for-sale securities, Fair Value	426,444	435,777
Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	1,682,202	1,843,511
Available-for-Sale, Gross Unrealized Gains	34,861	37,104
Available-for-Sale, Gross Unrealized Losses	87	53
Total available-for-sale securities, Fair Value	1,716,976	1,880,562
Non-Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	27,438	29,428
Available-for-Sale, Gross Unrealized Gains	3	2
Available-for-Sale, Gross Unrealized Losses	1,203	1,980
Total available-for-sale securities, Fair Value	26,238	27,450
Commercial Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	35,619	38,847
Available-for-Sale, Gross Unrealized Gains	1,275	1,533
Available-for-Sale, Gross Unrealized Losses	0	0
Total available-for-sale securities, Fair Value	36,894	40,380
Other Structured Financial Products [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	25,049	25,011
Available-for-Sale, Gross Unrealized Gains	0	0
Available-for-Sale, Gross Unrealized Losses	15,072	15,461	16,859
Total available-for-sale securities, Fair Value	9,977	9,550
Other Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	43,095	43,076
Available-for-Sale, Gross Unrealized Gains	2,777	2,643
Available-for-Sale, Gross Unrealized Losses	372	464
Total available-for-sale securities, Fair Value	45,500	45,255
Total Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	2,326,150	2,496,727
Available-for-Sale, Gross Unrealized Gains	67,328	74,908
Available-for-Sale, Gross Unrealized Losses	17,313	18,253
Total available-for-sale securities, Fair Value	2,376,165	2,553,382
Other Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	24,188	24,097
Available-for-Sale, Gross Unrealized Gains	931	1,179
Available-for-Sale, Gross Unrealized Losses	658	757
Total available-for-sale securities, Fair Value	$ 24,461	$ 24,519

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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-Publisher FASB

-Name FASB Staff Position (FSP)

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 13

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 14

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

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+ Details

- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References+ Details

- Definition

This item represents the gross unrealized gains for securities, at a point in time, which are categorized neither as held-to-maturity nor trading securities.

+ References+ Details