Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Statement of Comprehensive Income [Abstract]
Net income per consolidated statements of income	$ 147,365	$ 160,025	$ 150,460
Net unrealized gains (losses) on available for sale securities and transferred securities:
Net unrealized holding gains (losses) arising during the period	(37,090)	22,965	33,103
Change in net unrealized holding loss on securities transferred to held to maturity	1,985	2,383	2,704
Pension and other postretirement benefit plans:
Change in the actuarial loss of pension and other postretirement benefit plans	2,134	(3,846)	(4,278)
Reclassification adjustments for changes realized in net income:
Net change in prior service costs	84	112	187
Recognized net loss due to lump sum settlements	137	89	235
Change in net actuarial loss	1,241	846	597
Derivatives:
Change in the accumulated gain (loss) on effective cash flow hedge derivatives			(109)
Reclassification adjustment for (gain) loss realized in net income			(360)
Other comprehensive income (loss), net of tax	(31,509)	22,549	32,079
Comprehensive income	$ 115,856	$ 182,574	$ 182,539