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Derivative Instruments and Hedge Activities - Additional Information (Details) - USD ($)
 12 Months Ended
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