Investment Securities Schedule of Amortized Cost and Fair Values of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Statement [Line Items]
Held-to-maturity Securities	$ 6,608	$ 6,669
Held-to-maturity Securities, Unrecognized Holding Gain	39	44
Held-to-maturity Securities, Unrecognized Holding Loss	(21)	(14)
Held-to-maturity Securities, Fair Value	6,626	6,699
Available-for-sale Securities, Amortized Cost Basis	3,036,717	2,633,226
Available-for-sale Securities, Gross Unrealized Gains	77,509	74,424
Available-for-sale Securities, Gross Unrealized Losses	(31,427)	(34,352)
Available-for-sale Securities	3,082,799	2,673,298
Equity Securities [Member]
Statement [Line Items]
Available-for-sale Securities, Amortized Cost Basis	110,336	117,486
Available-for-sale Securities, Gross Unrealized Gains	3,811	2,383
Available-for-sale Securities, Gross Unrealized Losses	(1,028)	(2,819)
Available-for-sale Securities	113,119	117,050
U.S. Government Securities [Member]
Statement [Line Items]
Available-for-sale Securities, Amortized Cost Basis	330	334
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities	330	334
U.S. Government-Sponsored Agency Securities [Member]
Statement [Line Items]
Available-for-sale Securities, Amortized Cost Basis	3,980	3,987
Available-for-sale Securities, Gross Unrealized Gains	71	87
Available-for-sale Securities, Gross Unrealized Losses	(1)	(1)
Available-for-sale Securities	4,050	4,073
State and Municipal Securities [Member]
Statement [Line Items]
Available-for-sale Securities, Amortized Cost Basis	296,231	306,186
Available-for-sale Securities, Gross Unrealized Gains	14,437	15,832
Available-for-sale Securities, Gross Unrealized Losses	(36)	0
Available-for-sale Securities	310,632	322,018
Corporate Debt Securities [Member]
Statement [Line Items]
Available-for-sale Securities, Amortized Cost Basis	132,686	132,855
Available-for-sale Securities, Gross Unrealized Gains	6,235	4,979
Available-for-sale Securities, Gross Unrealized Losses	(11,341)	(14,528)
Available-for-sale Securities	127,580	123,306
Collateralized Mortgage Obligations [Member]
Statement [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,077,326	982,851
Available-for-sale Securities, Gross Unrealized Gains	19,678	19,186
Available-for-sale Securities, Gross Unrealized Losses	(419)	(828)
Available-for-sale Securities	1,096,585	1,001,209
Mortgage-Backed Securities [Member]
Statement [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,174,146	848,675
Available-for-sale Securities, Gross Unrealized Gains	33,126	31,837
Available-for-sale Securities, Gross Unrealized Losses	(646)	(415)
Available-for-sale Securities	1,206,626	880,097
Auction Rate Securities [Member]
Statement [Line Items]
Available-for-sale Securities, Amortized Cost Basis	241,682	240,852
Available-for-sale Securities, Gross Unrealized Gains	151	120
Available-for-sale Securities, Gross Unrealized Losses	(17,956)	(15,761)
Available-for-sale Securities	223,877	225,211
U.S. Government-Sponsored Agency Securities [Member]
Statement [Line Items]
Held-to-maturity Securities	6,001	5,987
Held-to-maturity Securities, Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Unrecognized Holding Loss	(21)	(14)
Held-to-maturity Securities, Fair Value	5,980	5,973
State and Municipal Securities [Member]
Statement [Line Items]
Held-to-maturity Securities	179	179
Held-to-maturity Securities, Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	179	179
Mortgage-Backed Securities [Member]
Statement [Line Items]
Held-to-maturity Securities	428	503
Held-to-maturity Securities, Unrecognized Holding Gain	39	44
Held-to-maturity Securities, Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	$ 467	$ 547

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading.

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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

- Definition

For an unclassified balance sheet, this item represents investments in debt securities which are categorized as held-to-maturity. The held-to-maturity category is for those securities that the entity has the positive intent and ability to hold until maturity.

+ References

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

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+ 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

- Definition

As of the balance sheet date, the excess of fair value over carrying value (amortized cost) of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding gain.

+ References+ Details

- Definition

As of the balance sheet date, the excess of carrying value (amortized cost) over fair value of a debt security categorized as held-to-maturity, exclusive of dividend or interest income recognized but not yet received and exclusive of any write-downs for other-than-temporary impairment. Such item represents the gross unrecognized holding loss.

+ References+ Details