Commitments, Off-Balance Sheet Arrangements and Contingent Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Commitments to Extend Credit [Member]
Summary of lending-related and other commitments
Lending related commitments	$ 4,551,151	[1],[2]	$ 4,561,210	[1],[2]
Commercial Letters Of Credit [Member]
Summary of lending-related and other commitments
Lending related commitments	48,479	[1]	47,699	[1]
Standby Letters of Credit [Member]
Summary of lending-related and other commitments
Lending related commitments	$ 313,165	[3]	$ 320,375	[3]

[1]  (1)        These off-balance sheet financial instruments are exercisable at the market rate prevailing at the date the underlying transaction will be completed and, thus, are deemed to have no current fair value, or the fair value is based on fees currently charged to enter into similar agreements and is not material at March 31, 2012 or December 31, 2011.

[2] (2)        Interest rate lock commitments to originate residential mortgage loans held for sale are considered derivative instruments and are disclosed in Note 10.

[3] (3)        The Corporation has established a liability of $4 million at both March 31, 2012 and December 31, 2011, as an estimate of the fair value of these financial instruments.