Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income per consolidated statements of income	$ 21,200	$ 54,440	$ 121,143	$ 108,808
Net unrealized gains (losses) on available for sale securities and transferred securities:
Net unrealized holding gains (losses) arising during the period	(9,407)	(5,781)	(20,798)	26,585
Change in net unrealized holding loss on securities transferred to held to maturity	477	603	1,562	1,832
Reclassification adjustments for changes realized in net income:
Net change in prior service costs	21	28	63	84
Recognized net loss due to lump sum settlement	137	30	137	60
Change in net actuarial loss	333	239	1,007	723
Other comprehensive income (loss), net of tax	(8,439)	(4,881)	(18,029)	29,284
Comprehensive income	$ 12,761	$ 49,559	$ 103,114	$ 138,092