CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 82,153	$ 74,554	$ 74,138
Securities AFS and transferred securities:
Change in unrealized holding gain (loss) on AFS securities during the period	105,845	87,481	(34,238)
Unrealized net gain on securities transferred from HTM to AFS under the transition guidance enumerated in ASU 2017-12	0	0	11,881
Change in net unrealized loss on securities transferred from HTM to AFS	0	0	401
Reclassification adjustment for amortization related to AFS and HTM debt securities	1,197	816	1,244
Reclassification adjustment for net (gain) loss on sale of AFS securities, included in net income	(8,257)	(756)	1,839
Derivatives:
Change in net unrealized (loss) gain on effective cash flow hedge interest rate swap derivatives	(23,462)	(9,118)	2,351
Reclassification adjustment of net loss (gain) related to derivatives designated as cash flow hedges	3,945	(2,043)	(1,406)
Pension plans:
Amortization of net actuarial loss and prior service credit, included in net periodic benefit cost	3,028	2,378	2,182
Effect of settlement recognition	215	0	0
Prior service cost adjustment due to plan amendments	163	0	0
Change in net actuarial loss	(593)	(9,816)	(1,994)
Other comprehensive income (loss), before tax	82,081	68,942	(17,740)
Income tax (expense) benefit related to items of other comprehensive income (loss)	(17,237)	(14,478)	3,725
Other comprehensive income (loss), net of tax	64,844	54,464	(14,015)
Comprehensive income	$ 146,997	$ 129,018	$ 60,123