Supplemental Cash Flow Disclosures (Details) - USD ($) $ in Thousands			3 Months Ended						6 Months Ended
	Jan. 01, 2019	Jan. 01, 2018	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Cash paid during the period for:
Interest									$ 1,946	$ 1,137
Income taxes									3,790	4,800
Noncash investing activities:
Unrealized gains on unrecognized post-retirement costs			$ 14				$ 18		28	27
Unrealized holdings gain (loss) on securities			275				(171)		563	(428)
Unrealized (loss) gain on junior subordinated debentures			(542)				(272)		(1,247)	295
Adoption of ASU 2016-01: reclassification of unrealized gain on junior subordinated debentures to accumulated other comprehensive income		$ 1,482
Adoption of ASU 2016-01: recognition of previously unrealized losses within CRA Fund		$ 184
Adoption of ASU 2016-02: recognition of lease right-of-use (ROU) asset	$ 3,395								3,836
Adoption of ASU 2016-02: recognition of lease liability	$ 3,486
Dividend declared
Noncash investing activities:
Cash dividend declared			$ 1,865	$ 1,869	$ 1,859	$ 1,690	$ 1,519	$ 1,520	$ 1,865	$ 1,520