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Securities - Available-for-sale Securities in Continuous Loss Position (Details) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2018 USD ($) investment | Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | $ 82,247 | $ 67,058
Less than 12 Months, Gross Unrealized Losses | (1,799) | (475)
12 Months or Greater, Fair Value | 47,110 | 50,580
12 Months or Greater, Gross Unrealized Losses | (1,845) | (1,312)
Total, Fair Value | 129,357 | 117,638
Total, Gross Unrealized Losses | (3,644) | (1,787)
U.S. Government-sponsored enterprises (GSEs) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | 16,016 | 1,358
Less than 12 Months, Gross Unrealized Losses | (281) | (1)
12 Months or Greater, Fair Value | 13,287 | 13,420
12 Months or Greater, Gross Unrealized Losses | (563) | (431)
Total, Fair Value | 29,303 | 14,778
Total, Gross Unrealized Losses | $ (844) | (432)
Number of investments in unrealized loss positions | investment | 9 |
Municipal securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | $ 5,915 | 3,418
Less than 12 Months, Gross Unrealized Losses | (129) | (43)
12 Months or Greater, Fair Value | 2,077 | 2,112
12 Months or Greater, Gross Unrealized Losses | (136) | (104)
Total, Fair Value | 7,992 | 5,530
Total, Gross Unrealized Losses | $ (265) | (147)
Number of investments in unrealized loss positions | investment | 19 |
Other debt securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | $ 0 | 950
Less than 12 Months, Gross Unrealized Losses | 0 | (24)
12 Months or Greater, Fair Value | 924 | 0
12 Months or Greater, Gross Unrealized Losses | (51) | 0
Total, Fair Value | 924 | 950
Total, Gross Unrealized Losses | $ (51) | (24)
Number of investments in unrealized loss positions | investment | 1 |
Mortgage-backed securities (GSEs) [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 Months, Fair Value | $ 60,316 | 61,332
Less than 12 Months, Gross Unrealized Losses | (1,389) | (407)
12 Months or Greater, Fair Value | 30,822 | 35,048
12 Months or Greater, Gross Unrealized Losses | (1,095) | (777)
Total, Fair Value | 91,138 | 96,380
Total, Gross Unrealized Losses | $ (2,484) | $ (1,184)
Number of investments in unrealized loss positions | investment | 63 |

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- Definition Amount of unrealized loss on securities classified as available-for-sale that have been in a loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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- Definition Amount of unrealized loss on securities classified as available-for-sale. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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- Definition Amount of unrealized loss on investments in available-for-sale securities that have been in a loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 + Details
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