Investment Securities Schedule of Amortized Cost and Fair Values of Investment Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Statement of Investments [Line Items]
Held-to-maturity Securities	$ 257	$ 292
Held-to-maturity Securities, Fair Value	279	319
Available-for-sale Securities, Amortized Cost Basis	2,770,956	2,752,220
Available-for-sale Securities, Gross Unrealized Gains	69,945	74,497
Available-for-sale Securities, Gross Unrealized Losses	(29,054)	(32,992)
Available-for-sale Securities	2,811,847	2,793,725
Held-to-maturity Securities, Unrecognized Holding Gain	22	27
Held-to-maturity Securities, Unrecognized Holding Loss	0	0
Equity Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	117,624	118,465
Available-for-sale Securities, Gross Unrealized Gains	6,507	5,016
Available-for-sale Securities, Gross Unrealized Losses	(241)	(918)
Available-for-sale Securities	123,890	122,563
U.S. Government Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	325	325
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	0	0
Available-for-sale Securities	325	325
U.S. Government-Sponsored Agency Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	885	2,376
Available-for-sale Securities, Gross Unrealized Gains	10	21
Available-for-sale Securities, Gross Unrealized Losses	(1)	0
Available-for-sale Securities	894	2,397
State and Municipal Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	283,142	301,842
Available-for-sale Securities, Gross Unrealized Gains	12,221	13,763
Available-for-sale Securities, Gross Unrealized Losses	(170)	(86)
Available-for-sale Securities	295,193	315,519
Corporate Debt Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	112,221	112,162
Available-for-sale Securities, Gross Unrealized Gains	8,906	7,858
Available-for-sale Securities, Gross Unrealized Losses	(6,083)	(7,178)
Available-for-sale Securities	115,044	112,842
Collateralized Mortgage Obligations [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	1,293,745	1,195,234
Available-for-sale Securities, Gross Unrealized Gains	15,279	16,008
Available-for-sale Securities, Gross Unrealized Losses	(3,225)	(123)
Available-for-sale Securities	1,305,799	1,211,119
Mortgage Backed Securities, Other [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	789,048
Available-for-sale Securities, Gross Unrealized Gains	27,022
Available-for-sale Securities, Gross Unrealized Losses	(7)
Available-for-sale Securities	816,063
Mortgage-Backed Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis		847,790
Available-for-sale Securities, Gross Unrealized Gains		31,831
Available-for-sale Securities, Gross Unrealized Losses		0
Available-for-sale Securities		879,621
Auction Rate Securities [Member]
Statement of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	173,966	174,026
Available-for-sale Securities, Gross Unrealized Gains	0	0
Available-for-sale Securities, Gross Unrealized Losses	(19,327)	(24,687)
Available-for-sale Securities	$ 154,639	$ 149,339

Amount of investment in debt and equity securities 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

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

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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

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-Publisher AICPA

-Name Accounting Research Bulletin (ARB)

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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