Investment Securities (Details) (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2010
Securities available for sale
Available-for-sale Securities, Amortized Cost	$ 3,418,763	$ 2,933,619	$ 2,980,203
Available-for-sale Securities, Gross Unrealized Gains	91,992	74,693	105,483
Available-for-sale Securities, Gross Unrealized Losses	(12,483)	(21,272)	(18,134)
Available-for-sale Securities, Fair Value	3,498,272	2,987,040	3,067,552
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	80,857	59,962	65,160
Held-to-maturity Securities, Fair Value	80,857	59,962	65,160
US Treasury Securities [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost			50,000
Available-for-sale Securities, Fair Value			50,000
U.S. government agency debentures [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	370,649	399,122	326,338
Available-for-sale Securities, Gross Unrealized Gains	743	703	1,130
Available-for-sale Securities, Gross Unrealized Losses	(148)	(194)	21
Available-for-sale Securities, Fair Value	371,244	399,631	327,447
Residential Mortgage Backed Securities Issued By US Government Sponsored Enterprises [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	1,528,537	1,343,021	1,491,498
Available-for-sale Securities, Gross Unrealized Gains	60,524	52,230	72,850
Available-for-sale Securities, Gross Unrealized Losses	(90)	(547)	(63)
Available-for-sale Securities, Fair Value	1,588,971	1,394,704	1,564,285
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	1,061,393	814,774	761,197
Available-for-sale Securities, Gross Unrealized Gains	19,883	18,223	23,543
Available-for-sale Securities, Gross Unrealized Losses	(1,326)	(2,306)
Available-for-sale Securities, Fair Value	1,079,950	830,691	784,740
Non-agency [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	93,733	15,018	20
Available-for-sale Securities, Gross Unrealized Gains	114
Available-for-sale Securities, Gross Unrealized Losses			(1)
Available-for-sale Securities, Fair Value	93,847	15,018	19
Corporate debt securities [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	61,461	61,435	61,410
Available-for-sale Securities, Gross Unrealized Losses	(10,738)	(16,106)	(17,968)
Available-for-sale Securities, Fair Value	50,723	45,329	43,442
U.S. States and political subdivisions [Member]
Securities held to maturity
Held-to-maturity Securities, Amortized Cost	80,857	59,962	65,160
Held-to-maturity Securities, Fair Value	80,857	59,962	65,160
U.S. States and political subdivisions [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	299,238	296,327	286,297
Available-for-sale Securities, Gross Unrealized Gains	10,728	3,537	7,960
Available-for-sale Securities, Gross Unrealized Losses	(181)	(2,119)	(81)
Available-for-sale Securities, Fair Value	309,785	297,745	294,176
Total debt securities [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	3,415,011	2,929,697	2,976,760
Available-for-sale Securities, Gross Unrealized Gains	91,992	74,693	105,483
Available-for-sale Securities, Gross Unrealized Losses	(12,483)	(21,272)	(18,134)
Available-for-sale Securities, Fair Value	3,494,520	2,983,118	3,064,109
Marketable equity securities [Member]
Securities available for sale
Available-for-sale Securities, Amortized Cost	3,752	3,922	3,443
Available-for-sale Securities, Fair Value	$ 3,752	$ 3,922	$ 3,443

For an unclassified balance sheet, this item represents investments in debt and equity securities which are 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 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 3: 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 4: 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 5: 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 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 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.

Reference 8: 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 9: 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 10: 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=6379932&loc=d3e22054-111558

+ 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

- Definition

This item represents the aggregate fair value of investments in debt securities as of the balance sheet date and which are categorized as held-to-maturity.

+ References+ Details