CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 21,317	$ 21,554	$ 55,408	$ 25,507
Securities AFS and transferred securities:
Change in unrealized holding gain (loss) on AFS securities during the period	33,166	25,813	(15,813)	87,299
Reclassification adjustment for amortization related to AFS and HTM debt securities	390	215	806	336
Reclassification adjustment for net gain on sale of AFS securities, included in net income	(15)	(2,662)	(2,018)	(8,203)
Derivatives:
Change in net unrealized (loss) gain on effective cash flow hedge interest rate swap derivatives	(3,104)	(5,439)	7,919	(25,039)
Reclassification adjustment of net loss related to derivatives designated as cash flow hedges	1,599	797	3,167	696
Pension plans:
Amortization of net actuarial (gain) loss and prior service credit, included in net periodic benefit cost	(9)	661	632	1,388
Prior service cost adjustment due to plan amendment	0	163	0	163
Change in net actuarial loss	0	(7,558)	0	(7,558)
Other comprehensive income (loss), before tax	32,027	11,990	(5,307)	49,082
Income tax (expense) benefit related to items of other comprehensive income (loss)	(6,726)	(2,518)	1,114	(10,307)
Other comprehensive income (loss), net of tax	25,301	9,472	(4,193)	38,775
Comprehensive income	$ 46,618	$ 31,026	$ 51,215	$ 64,282