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Accumulated Other Comprehensive Income (Loss) (Components of unrealized holding gains on AFS securities) (Details) - USD ($) $ in Thousands | 3 Months Ended
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Mar. 31, 2018 | Mar. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Unrealized gains (losses) on AFS securities arising during the period | $ (8,057) | $ 1,677
Tax effect | 1,684 | (450)
Unrealized gains (losses), net of tax | (6,277) | 1,238
Unrealized Holding Gains (Losses) on AFS Securities [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Unrealized gains (losses) on AFS securities arising during the period | (8,057) | 1,677
Tax effect | 1,684 | (450)
Unrealized gains (losses), net of tax | (6,373) | 1,227
Unrealized Holding Gains (Losses) on AFS Securities [Member] | Auction Rate Money Market Preferred and Preferred Stocks [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Unrealized gains (losses) on AFS securities arising during the period | (37) | 355
Tax effect | 0 | 0
Unrealized gains (losses), net of tax | (37) | 355
Unrealized Holding Gains (Losses) on AFS Securities [Member] | All Other AFS Securities [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Unrealized gains (losses) on AFS securities arising during the period | (8,020) | 1,322
Tax effect | 1,684 | (450)
Unrealized gains (losses), net of tax | (6,336) | 872
Accumulated Defined Benefit Plans Adjustment [Member] |  |
Accumulated Other Comprehensive Income (Loss) [Line Items] |  |
Unrealized gains (losses), net of tax | $ 0 | $ 0

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- Definition Amount of tax expense (benefit), after reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e640-108580 + Details
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- Definition Amount after tax and reclassification adjustments of other comprehensive income (loss). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1A -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669619-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1B -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669625-108580 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=66004921&loc=d3e1436-108581 + Details
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- Definition Amount before tax and reclassification adjustments of unrealized holding gain (loss) on available-for-sale securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=66004124&loc=d3e637-108580 + Details
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