Accumulated Other Comprehensive Income (''AOCI'') - Amount Reclassified from AOCI (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Amount Reclassified from AOCI
Gain on sales of securities	$ 170		$ 548		$ 270	$ 548
Interest income on taxable securities	3,155		4,136		7,103	8,645
Income tax expense	(4,274)		(4,623)		(5,142)	(9,130)
Net income	10,618	$ 1,861	11,353	$ 12,146	12,479	23,499
Amount Reclassified from AOCI
Amount Reclassified from AOCI
Other noninterest expense					(160)	(43)
Income tax benefit					48	13
Net of tax					(112)	(30)
Unrealized Gains (Losses) on Available-for-Sale Securities and I/O Strips
Amount Reclassified from AOCI
Net of tax	120		386		191	386
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	170		548		270	548
Income tax expense	(50)		(162)		(79)	(162)
Net income	120		386		191	386
Unamortized Unrealized Gain on Available-for-Sale Securities Reclassified to Held-to-Maturity
Amount Reclassified from AOCI
Net of tax	9		9		18	27
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		26	39
Income tax expense	(4)		(4)		(8)	(12)
Net income	9		9		18	27
Defined Benefit Pension Plan Items
Amount Reclassified from AOCI
Net of tax	(63)		(15)		(112)	(30)
Defined Benefit Pension Plan Items | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Other noninterest expense	(90)		(22)
Income tax benefit	27		7
Net of tax	(63)		(15)
Prior transition obligation | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Other noninterest expense	15		24		30	49
Actuarial losses | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Other noninterest expense	(105)		(46)		(190)	(92)
Accumulated Other Comprehensive Income / (Loss)
Amount Reclassified from AOCI
Net of tax	66		380		97	383
Accumulated Other Comprehensive Income / (Loss) | Amount Reclassified from AOCI
Amount Reclassified from AOCI
Net of tax	$ 66		$ 380		$ 97	$ 383