Accumulated Other Comprehensive Income (''AOCI'') - Amount Reclassified from AOCI (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Amount Reclassified from AOCI
Gain on sales of securities				$ 330			$ 270	$ 878
Interest income on taxable securities	$ 2,481			3,504			9,584	12,149
Income tax expense	(4,198)			(4,633)			(9,340)	(13,763)
Net income	11,197	$ 10,618	$ 1,861	11,277	$ 11,353	$ 12,146	23,676	34,776
Amount Reclassified from AOCI
Amount Reclassified from AOCI
Other noninterest expense							(445)	(65)
Income tax benefit							132	19
Net of tax							(313)	(46)
Unrealized Gains (Losses) on Available-for-Sale Securities and I/O Strips
Amount Reclassified from AOCI
Net of tax				232			191	618
Unrealized Gains (Losses) on Available-for-Sale Securities and I/O Strips | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Gain on sales of securities				330			270	878
Income tax expense				(98)			(79)	(260)
Net income				232			191	618
Unamortized Unrealized Gain on Available-for-Sale Securities Reclassified to Held-to-Maturity
Amount Reclassified from AOCI
Net of tax	9			9			27	36
Unamortized Unrealized Gain on Available-for-Sale Securities Reclassified to Held-to-Maturity | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Interest income on taxable securities	13			13			39	52
Income tax expense	(4)			(4)			(12)	(16)
Net income	9			9			27	36
Defined Benefit Pension Plan Items
Amount Reclassified from AOCI
Net of tax	(201)			(16)			(313)	(46)
Defined Benefit Pension Plan Items | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Other noninterest expense	(285)			(22)
Income tax benefit	84			6
Net of tax	(201)			(16)
Prior transition obligation | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Other noninterest expense	(184)			24			(154)	73
Actuarial losses | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Other noninterest expense	(101)			(46)			(291)	(138)
Accumulated Other Comprehensive Income / (Loss)
Amount Reclassified from AOCI
Net of tax	(192)			225			(95)	608
Accumulated Other Comprehensive Income / (Loss) | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Net of tax	$ (192)			$ 225			$ (95)	$ 608