Fair Value Option Summary of Corporation's Mortgage Loans Held for Sale (Details) (USD $)			3 Months Ended	9 Months Ended
Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Mortgage Loans Held For Sale [Member]	Sep. 30, 2011 Mortgage Loans Held For Sale [Member]	Sep. 30, 2012 Mortgage Loans Held For Sale [Member]	Sep. 30, 2011 Mortgage Loans Held For Sale [Member]	Sep. 30, 2012 Mortgage Loans Held For Sale [Member] Cost [Member]	Dec. 31, 2011 Mortgage Loans Held For Sale [Member] Cost [Member]	Sep. 30, 2012 Mortgage Loans Held For Sale [Member] Fair Value	Dec. 31, 2011 Mortgage Loans Held For Sale [Member] Fair Value
Fair Value, Option, Quantitative Disclosures [Line Items]
Loans Held-for-sale, Mortgages	$ 85,477,000	$ 47,009,000					$ 81,304,000	$ 45,324,000	$ 85,477,000	$ 47,009,000
Gain (loss) in fair values of mortgage loans held for sale			$ 1,500,000	$ 1,500,000	$ 2,500,000	$ 3,300,000

This item represents, for each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings during the period and in which line in the income statement those gains and losses are reported. This item may also include amounts of gains and losses for other items measured at fair value, but for which the fair value option has not been elected (for instance, items required to be measured at fair value).

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 159

-Paragraph 19

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 30

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14172-108612

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration