Loans Receivable and Credit Quality Troubled Debt Restructured Loans (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Loans	Dec. 31, 2016 USD ($) Loans
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans	1	9
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 108	$ 10,369
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 109	$ 10,206
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | Loans	0	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 1,276
Commercial Loan [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans	0	3
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 0	$ 7,384
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 7,209
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0
Commercial Loan [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		2
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 7,209
Commercial Loan [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Loan [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Loan [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		1
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Tax Exempt [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 0	$ 0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0
Commercial Tax Exempt [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Tax Exempt [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Tax Exempt [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Tax Exempt [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Real Estate Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans	0	1
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 0	$ 1,276
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 1,276
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | Loans	0	1
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 1,276
Commercial Real Estate Portfolio Segment [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Real Estate Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Real Estate Portfolio Segment [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Commercial Real Estate Portfolio Segment [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		1
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 1,276
Construction Loans [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 0	$ 0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0
Construction Loans [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Construction Loans [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Construction Loans [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Construction Loans [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Residential Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans	1	5
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 108	$ 1,709
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 109	$ 1,721
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0
Residential Portfolio Segment [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Residential Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		4
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 519
Residential Portfolio Segment [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		1
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 1,202
Residential Portfolio Segment [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Home Equity Line of Credit [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 0	$ 0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0
Home Equity Line of Credit [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Home Equity Line of Credit [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Home Equity Line of Credit [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Home Equity Line of Credit [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Consumer Portfolio Segment [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Pre-Modification Recorded Investment	$ 0	$ 0
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 0	$ 0
Financing Receivable, Modifications, Subsequent Default, Number of Contracts | Loans	0	0
Financing Receivable, Modifications, Subsequent Default, Recorded Investment	$ 0	$ 0
Consumer Portfolio Segment [Member] | Extended Maturity [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Consumer Portfolio Segment [Member] | Contractual Interest Rate Reduction [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Consumer Portfolio Segment [Member] | Payment Deferral [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0
Consumer Portfolio Segment [Member] | Combination of Concessions [Member]
Financing Receivable, Modifications [Line Items]
Financing Receivable, Modifications, Number of Contracts | Loans		0
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 0