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Derivative Instruments and Hedge Activities - Summary of Derivative Financial Instruments and Classification on Consolidated Statements of Financial Condition (Details) - USD ($) | Dec. 31, 2017 | Dec. 31, 2016
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Derivatives Fair Value [Line Items] |  |
Notional Amount | $ 344,726,000 | $ 151,213,000
Other Assets | 5,981,000 | 4,317,000
Other Liabilities | 994,000 | 559,000
Cash Flow Hedges |  |
Derivatives Fair Value [Line Items] |  |
Notional Amount | 250,000,000 |
Other Assets | 5,030,000 |
Other Liabilities | 38,000 |
Other Interest Rate Swaps |  |
Derivatives Fair Value [Line Items] |  |
Notional Amount | 94,726,000 |
Other Assets | 951,000 |
Other Liabilities | 956,000 |
Derivatives Designated as Hedging Instruments | Interest Rate Swaps | Cash Flow Hedges |  |
Derivatives Fair Value [Line Items] |  |
Notional Amount | 250,000,000 | 100,000,000
Other Assets | 5,030,000 | 3,719,000
Other Liabilities | 38,000 |
Derivatives Not Designated As Hedging Instruments | Other Interest Rate Swaps |  |
Derivatives Fair Value [Line Items] |  |
Notional Amount | 94,726,000 | 51,213,000
Other Assets | 951,000 | 598,000
Other Liabilities | $ 956,000 | $ 559,000

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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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