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Derivative Instruments and Hedge Activities - Additional Information (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Derivative [Line Items] |  |  |
Derivative notional amount | $ 344,726,000 | $ 151,213,000 |
Unrealized gain (loss) to be reclassified as an increase to interest expense during the next twelve months | 512,000 |  |
Credit valuation adjustment decrease, increase to non-interest income | (44,000) | 39,000 | $ 0
Cash Flow Hedges |  |  |
Derivative [Line Items] |  |  |
Derivative notional amount | 250,000,000 |  |
Other Interest Rate Swaps |  |  |
Derivative [Line Items] |  |  |
Derivative notional amount | $ 94,726,000 |  |
Derivative maturity date, start year | Jan. 31, 2020 |  |
Derivative maturity date, end year | Nov. 30, 2027 |  |
Derivative instruments transaction fees | $ 393,000 | 679,000 | $ 0
Derivatives Designated as Hedging Instruments | Interest Rate Swaps | Cash Flow Hedges |  |  |
Derivative [Line Items] |  |  |
Derivative notional amount | 250,000,000 | 100,000,000 |
Federal Home Loan Bank Advances | Interest Rate Swaps |  |  |
Derivative [Line Items] |  |  |
Interest expense on swap transaction | 579,000 | 40,000 |
Federal Home Loan Bank Advances | Derivatives Designated as Hedging Instruments | Interest Rate Swaps | Cash Flow Hedges |  |  |
Derivative [Line Items] |  |  |
Derivative notional amount | $ 250,000,000 | $ 100,000,000 |

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- Definition Derivative instruments changes in credit valuation adjustment recognized in non interest income. + References No definition available. + Details
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- Definition Derivative instruments transaction fees. + References No definition available. + Details
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- Definition Interest expense on swap transaction. + References No definition available. + Details
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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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- Definition The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=35736893&loc=d3e80748-113994 + Details
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