Fair Value Measurements Changes in Assets and Liabilities Measured at Fair Value on a Recurring Basis Using Level 3 Inputs (Details) (Fair Value, Measurements, Recurring [Member], Fair Value, Inputs, Level 3 [Member], USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2011		Sep. 30, 2010		Sep. 30, 2011		Sep. 30, 2010		Dec. 31, 2010
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, end of period	$ 240,702,000				$ 240,702,000
Single-issuer Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	7,819,000		8,085,000		8,583,000		6,981,000
Transfer to Level 3 from Level 2							650,000	[1]
Realized adjustment to fair value	0	[2]	0	[2]	0	[2]	0	[2]
Unrealized adjustment to fair value	(1,235,000)	[3]	466,000	[3]	(1,197,000)	[3]	919,000	[3]
Sales			0				0
Redemptions	0		0		0		0
(Premium amortization) discount accretion	(1,000)	[4]	0	[4]	(3,000)	[4]	1,000	[4]
Transfers from Level 3 to Level 2					(800,000)	[1]
Balance, end of period	6,583,000		8,551,000		6,583,000		8,551,000
Investments, Fair Value Disclosure									800,000
Pooled Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	5,433,000		4,279,000		4,528,000		4,979,000
Transfer to Level 3 from Level 2							0	[1]
Realized adjustment to fair value	(53,000)	[2]	(2,335,000)	[2]	(1,406,000)	[2]	(9,477,000)	[2]
Unrealized adjustment to fair value	12,000	[3]	2,805,000	[3]	2,564,000	[3]	9,258,000	[3]
Sales			0				0
Redemptions	(117,000)		(328,000)		(409,000)		(328,000)
(Premium amortization) discount accretion	0	[4]	20,000	[4]	(2,000)	[4]	9,000	[4]
Transfers from Level 3 to Level 2					0	[1]
Balance, end of period	5,275,000		4,441,000		5,275,000		4,441,000
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	255,142,000		276,539,000		260,679,000		289,203,000
Transfer to Level 3 from Level 2							0	[1]
Realized adjustment to fair value	(292,000)	[2]	0	[2]	(292,000)	[2]	0	[2]
Unrealized adjustment to fair value	(14,660,000)	[3]	(704,000)	[3]	(22,139,000)	[3]	(4,346,000)	[3]
Sales			(10,233,000)				(15,266,000)
Redemptions	(318,000)		(1,470,000)		(569,000)		(7,852,000)
(Premium amortization) discount accretion	830,000	[4]	1,163,000	[4]	3,023,000	[4]	3,556,000	[4]
Transfers from Level 3 to Level 2					0	[1]
Balance, end of period	$ 240,702,000		$ 265,295,000		$ 240,702,000		$ 265,295,000

[1] During the nine months ended September 30, 2011, one single-issuer trust preferred security with a fair value of $800,000 as of December 31, 2010 was reclassified as a Level 2 asset. As of September 30, 2011, the fair value of this security was measured by a third-party pricing service using both quoted prices for similar assets and model-based valuation techniques that derived fair value based on market-corroborated data, such as instruments with similar prepayment speeds and default interest rates. As of December 31, 2010, the fair value of this security was determined based on quotes provided by third-party brokers who determined its fair value based predominantly on an internal valuation model.

[2] For pooled trust preferred securities and ARCs, realized adjustments to fair value represent credit related other-than-temporary impairment charges that were recorded as a reduction to investment securities gains (losses) on the consolidated statements of income.

[3] Pooled trust preferred securities, single-issuer trust preferred securities and ARCs are classified as available for sale investment securities; as such, the unrealized adjustment to fair value was recorded as an unrealized holding gain (loss) and included as a component of available for sale investment securities on the consolidated balance sheet.

[4] Included as a component of net interest income on the consolidated statements of income.