Investment Securities (Amortized Cost and Fair Values of Investment Securities) (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	$ 2,345,501	$ 2,520,824
Available-for-Sale, Gross Unrealized Gains	33,142	76,087
Available-for-Sale, Gross Unrealized Losses	35,214	19,010
Total available-for-sale securities, Fair Value	2,343,429	2,577,901
U.S. Government Agencies [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	60,189	113,367
Available-for-Sale, Gross Unrealized Gains	412	1,041
Available-for-Sale, Gross Unrealized Losses	535	0
Total available-for-sale securities, Fair Value	60,066	114,408
Obligations Of States And Political Subdivisions [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	396,320	403,487
Available-for-Sale, Gross Unrealized Gains	15,338	32,585
Available-for-Sale, Gross Unrealized Losses	4,158	295
Total available-for-sale securities, Fair Value	407,500	435,777
Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	1,738,829	1,843,511
Available-for-Sale, Gross Unrealized Gains	15,559	37,104
Available-for-Sale, Gross Unrealized Losses	13,856	53
Total available-for-sale securities, Fair Value	1,740,532	1,880,562
Non-Agency Residential Mortgage-Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	25,929	29,428
Available-for-Sale, Gross Unrealized Gains	1	2
Available-for-Sale, Gross Unrealized Losses	747	1,980
Total available-for-sale securities, Fair Value	25,183	27,450
Commercial Mortgage Backed Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	31,895	38,847
Available-for-Sale, Gross Unrealized Gains	890	1,533
Available-for-Sale, Gross Unrealized Losses	0	0
Total available-for-sale securities, Fair Value	32,785	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	14,543	15,461	16,462
Total available-for-sale securities, Fair Value	10,506	9,550
Other Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	43,115	43,076
Available-for-Sale, Gross Unrealized Gains	558	2,643
Available-for-Sale, Gross Unrealized Losses	470	464
Total available-for-sale securities, Fair Value	43,203	45,255
Total Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	2,321,326	2,496,727
Available-for-Sale, Gross Unrealized Gains	32,758	74,908
Available-for-Sale, Gross Unrealized Losses	34,309	18,253
Total available-for-sale securities, Fair Value	2,319,775	2,553,382
Other Equity Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
Available-for-Sale, Amortized Cost	24,175	24,097
Available-for-Sale, Gross Unrealized Gains	384	1,179
Available-for-Sale, Gross Unrealized Losses	905	757
Total available-for-sale securities, Fair Value	$ 23,654	$ 24,519

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

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7534914&loc=d3e22054-111558

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 16

-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 5: 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 6: 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 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 22

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

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15D

-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 FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15E

-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 FASB Staff Position (FSP)

-Number FAS115-1/124-1

-Paragraph 15C

-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.

+ 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