Comprehensive Income/(Loss) (Changes in AOCI) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Changes in accumulated other comprehensive (loss) income by component, net of tax
Balance beginning of period	$ 910,619	$ 812,583	$ 702,749
Other comprehensive income (loss)	11,743	(3,510)	(1,069)
Balance end of period	945,606	910,619	812,583
Accumulated Other Comprehensive Income (Loss)
Changes in accumulated other comprehensive (loss) income by component, net of tax
Balance beginning of period	(9,460)	(5,950)	(3,818)
Other comprehensive income (loss)	11,743	(3,510)	(1,069)
Reclassification due to the adoption of ASU No. 2018-02		0	(1,063)
Balance end of period	2,283	(9,460)	(5,950)
Investment Securities Available-for-Sale
Changes in accumulated other comprehensive (loss) income by component, net of tax
Balance beginning of period	(9,712)	(6,113)	(4,213)
Other comprehensive income (loss)	11,911	(3,599)	(817)
Reclassification due to the adoption of ASU No. 2018-02		0	(1,083)
Balance end of period	2,199	(9,712)	(6,113)
Postretirement Benefits
Changes in accumulated other comprehensive (loss) income by component, net of tax
Balance beginning of period	252	163	395
Other comprehensive income (loss)	(168)	89	(252)
Reclassification due to the adoption of ASU No. 2018-02		0	20
Balance end of period	$ 84	$ 252	$ 163