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Investment Securities Held to Maturity Securities by Type (Details) - USD ($) $ in Thousands | Sep. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Schedule of Held-to-maturity Securities [Line Items] |  |
Held-to-maturity Securities | $ 436,081 | $ 372,513
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain | 770 | 60
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss | (1,969) | (3,955)
Securities held to maturity, fair value | 434,882 | 368,618
US Government Agencies Residential Mortgage-backed Securities [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held-to-maturity Securities | 4,113 | 4,297
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain | 5 | 0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss | 0 | (4)
Securities held to maturity, fair value | 4,118 | 4,293
US Government Agency Debt Securities Commercial [Domain] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held-to-maturity Securities | 58,528 | 34,444
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain | 0 | 0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss | (861) | (561)
Securities held to maturity, fair value | 57,667 | 33,883
Residential Mortgage Backed Securities [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held-to-maturity Securities | 318,442 | 280,430
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain | 367 | 5
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss | (975) | (2,527)
Securities held to maturity, fair value | 317,834 | 277,908
Obligations of U.S. Government-Sponsored Enterprises - Mortgage-Backed Securities - Commercial [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held-to-maturity Securities | 14,226 | 14,675
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain | 0 | 0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss | (4) | (142)
Securities held to maturity, fair value | 14,222 | 14,533
Obligations of States and Political Subdivisions [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held-to-maturity Securities | 40,572 | 38,667
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain | 398 | 55
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss | (129) | (721)
Securities held to maturity, fair value | 40,841 | 38,001
Foreign Government Debt Securities [Member] |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Held-to-maturity Securities | 200 | 0
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain | 0 | 0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss | 0 | 0
Securities held to maturity, fair value | $ 200 | $ 0

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- Definition Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.1) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.6) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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- Definition Amount of accumulated unrealized gain on investments in debt securities classified as held-to-maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563 + Details
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- Definition Amount of accumulated unrealized loss on investments in debt securities classified as held-to-maturity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27232-111563 + Details
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