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Securities - Narrative (Details) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2018 USD ($) security institution | Mar. 31, 2017 USD ($) | Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available for sale debt securities | $ 961,589,000 | $ 2,496,000 | $ 674,104,000
Sale proceeds |  | $ 2,496,000 |
Fair Value | $ 948,365,000 |  | 671,488,000
Number of institutions issuing debt (more than) | institution | 160 |  |
Trust preferred securities |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available for sale debt securities | $ 12,429,000 |  | 12,442,000
Fair Value | $ 10,045,000 |  | 9,388,000
Number of securities representing interests in tranches of trusts (tranches) | security | 2 |  |
Impairments | $ 0 |  |
Secure government, public and trust deposits |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available for sale securities pledged as collateral | 259,688,000 |  | 217,867,000
Short-term borrowings |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available for sale securities pledged as collateral | 20,644,000 |  | 25,888,000
Trust preferred securities |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available for sale debt securities | 12,429,000 |  | 12,442,000
Fair Value | 10,045,000 |  | 9,388,000
Government agency mortgage backed securities | Residential mortgage-backed securities |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available for sale debt securities | 416,954,000 |  | 196,121,000
Fair Value | 409,470,000 |  | 193,950,000
Government agency collateralized mortgage obligations | Residential mortgage-backed securities |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available for sale debt securities | 244,213,000 |  | 180,258,000
Fair Value | 237,666,000 |  | 176,639,000
Obligations of states and political subdivisions |  |  |
Schedule of Available-for-sale Securities [Line Items] |  |  |
Available for sale debt securities | 222,814,000 |  | 228,589,000
Fair Value | $ 226,342,000 |  | $ 234,481,000

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- Definition This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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