Acquisition of IA Bancorp, Inc. (Narrative) (Details)		3 Months Ended		5 Months Ended	9 Months Ended
	Apr. 17, 2018 item	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 USD ($)
Business Acquisition [Line Items]
Amortization expense		$ 19,000			$ 39,000
Merger related costs		$ 119,000			$ 2,303,000
Core Deposit Intangibles [Member]
Business Acquisition [Line Items]
Intangible asset, useful life					10 years
Amortization expense				$ 39,000
Certificates of Deposit [Member]
Business Acquisition [Line Items]
Amortization period of fair value adjustment					5 years
IA Bancorp [Member]
Business Acquisition [Line Items]
Share exchange rate	0.189
Fair value adjustment on pools of homogeneous loans, interest rate discount					$ 1,900,000
Number of series of shares issued | item	2
Number of series of shares acquired | item	2
Fair value adjustment on pools of homogeneous loans, credit discount					3,900,000
Merger related costs			$ 800,000		2,300,000
Merger related costs, early termination fees					2,000,000
IA Bancorp [Member] | Certificates of Deposit [Member]
Business Acquisition [Line Items]
Fair value adjustment, liabilities					$ 751,000