Derivative Instruments (Fair Value of the Corporation's Derivative Financial Instruments and Their Classification on the Balance Sheet) (Details) (Interest Rate Contract [Member], USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Other Assets [Member]
Asset derivatives	$ 29,333	$ 25,631
Other Liabilities [Member]
Liability derivatives	$ 29,326	$ 25,043

Fair value of a derivative liability that is not designated or qualifying as a hedging instrument, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 205G

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 133
-Paragraph 44C
-Subparagraph a
-Clause 1

Name:	us-gaap_DerivativeLiabilityNotDesignatedAsHedgingInstrumentFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant