Other Comprehensive Income (Loss) - Reclassification out of AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gain on securities transactions	$ 0	$ 1,256	$ 370	$ 1,721
Other non-interest expense	5,848	2,217	14,756	7,927
Income before income tax expense	20,339	19,610	49,056	53,702
Income (tax) benefit	(5,252)	(5,392)	(12,107)	(12,534)
Net of tax	15,087	14,218	36,949	41,168
Accumulated Other Comprehensive Income (Loss) Components
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income before income tax expense	(1,071)	326	(2,843)	(1,058)
Income (tax) benefit	225	(96)	593	187
Net of tax	(846)	230	(2,250)	(871)
Accumulated Other Comprehensive Income (Loss) Components | Reclassification adjustment for gains included in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Gain on securities transactions	0	1,256	370	1,721
Accumulated Other Comprehensive Income (Loss) Components | Reclassification adjustment of actuarial net (loss) included in net income
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other non-interest expense	$ (1,071)	$ (930)	$ (3,213)	$ (2,779)