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 $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Pooled Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 4,528		$ 4,979
Transfers from Level 3 to Level 2	0	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			0
Realized adjustment to fair value	(1,406)	[2]	(11,969)	[2]
Unrealized adjustment to fair value	2,465	[3]	11,842	[3]
Sales	0	[4]	0
Settlements - calls			(328)
(Premium amoritization)/discount accretion	(2)	[5]	4	[4]
Balance, end of period	5,109		4,528
Pooled Trust Preferred Securities [Member] | Securities by Contractual Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Settlements - calls	0
Pooled Trust Preferred Securities [Member] | Call Option [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Settlements - calls	(476)
Single-issuer Trust Preferred Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	8,583		6,981
Transfers from Level 3 to Level 2	(800)	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3			650
Realized adjustment to fair value	0	[2]	0	[2]
Unrealized adjustment to fair value	28	[3]	951	[3]
Sales	0	[4]	0
Settlements - calls			0
(Premium amoritization)/discount accretion	(1)	[5]	1	[4]
Balance, end of period	4,180		8,583
Single-issuer Trust Preferred Securities [Member] | Securities by Contractual Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Settlements - calls	1,650
Single-issuer Trust Preferred Securities [Member] | Call Option [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Settlements - calls	(1,980)
Auction Rate Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	260,679		289,203
Transfers from Level 3 to Level 2	0	[1]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3
Realized adjustment to fair value	(292)	[2]	0	[2]
Unrealized adjustment to fair value	(4,383)	[3]	(10,850)	[3]
Sales	0	[4]	(15,266)
Settlements - calls			(8,969)
(Premium amoritization)/discount accretion	4,051	[5]	6,561	[4]
Balance, end of period	225,211		260,679
Auction Rate Securities [Member] | Securities by Contractual Maturities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Settlements - calls
Auction Rate Securities [Member] | Call Option [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Settlements - calls	$ (34,844)

[1] )During the year ended December 31, 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 December 31, 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 mode

[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 on the consolidated statements of incom

[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] During the year ended December 31, 2011, the Corporation sold one pooled trust preferred security with a par value of $6.4 million and a book value of zero for no gain or loss. This security had a book value of zero as a result of prior year other-than-temporary impairment charges.

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