Accumulated Other Comprehensive Income (Loss) - Other Comprehensive Loss and Related Tax Effects (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss)
Unrealized gain (loss) on investment securities available-for-sale	$ 8,779	$ 5,109	$ (2,014)
Net gain on the sale of investment securities available-for-sale	(918)	(23)
Other comprehensive income on available-for-sale debt securities	7,861	5,086	(2,014)
Amortization of actuarial loss (2)	218	227	194
Actuarial gain (loss)	(1,616)	412	(785)
Change in benefit plan liabilities	(1,398)	639	(591)
Net change in derivatives	315	441	246
Other comprehensive income (loss)	6,778	6,166	(2,359)
Income tax (benefit)	1,424	1,295	(496)
Other comprehensive income (loss)	$ 5,354	$ 4,871	$ (1,863)

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