Loans - Narrative (Details) $ in Thousands		3 Months Ended	9 Months Ended	12 Months Ended
	Jul. 01, 2017 USD ($)	Jun. 30, 2017 Contract	Sep. 30, 2017 USD ($) Contract	Dec. 31, 2016 USD ($) Contract	Dec. 31, 2013 Contract
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for order of valuations (at least)			18 months
Number of loans moved to nonaccrual status		2
Number of troubled debt restructured loan paid off			1	1
Number of loans which has periodic late payments			1
Number of loans classified as troubled debt restructured loans with active forbearance agreements			2
Number of forbearance agreements negotiated					1
Consumer mortgage loans secured by residential real estate properties for which formal foreclosure proceedings are in process | $			$ 1,109	$ 471
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 | $			$ 283	$ 74
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
Financing receivable, loan to value ratio of appraised value of property			80.00%
Maximum | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, term			30 years
Financing receivable, loan to value ratio of appraised value of property			80.00%
Maximum | Home equity lines of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, term			20 years
Financing receivable, loan to value ratio of appraised value of property			90.00%