Loans - Narrative (Details) $ in Thousands		3 Months Ended	12 Months Ended
	Jul. 01, 2017 USD ($)	Mar. 31, 2018 USD ($) Contract	Dec. 31, 2017 USD ($) Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for order of valuations (at least)		18 months
Number of troubled debt restructured loan paid off | Contract		1	1
Number of loans which has periodic late payments | Contract		1
Consumer mortgage loans secured by residential real estate properties for which formal foreclosure proceedings are in process		$ 1,475	$ 848
Residential mortgage and commercial loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due to discontinue accrual interest on financing receivable		90 days
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Threshold period past due for write-off of financing receivable (no later than)		120 days
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period of financing receivable, updated valuation on real estate secured loans, 90 days past due		90 days
Number of previous months with no updated valuation completed for corporation to update valuation		12 months
Impaired financing receivable, valuation on real estate collateralized loans		30 days
Entity Loan Modification Program
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds from paid off troubled debt restructured loans		$ 832	$ 283
New Windsor
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest rate fair value discount	$ 731
Credit fair value discount	$ 4,501
Maximum | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable term		20 years
Loan-to-value ratio (no greater than)		80.00%
Maximum | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable term		30 years
Loan-to-value ratio (no greater than)		80.00%
Loan-to-value ratio that requires private mortgage insurance (in excess of)		80.00%
Maximum | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable term		20 years
Loan-to-value ratio (no greater than)		90.00%