CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 27,074	$ 19,792	$ 52,581	$ 57,219
Securities available for sale and transferred securities:
Change in unrealized holding gain on available for sale securities during the period	1,601	17,334	88,900	96,156
Reclassification adjustment for amortization related to available for sale and held to maturity debt securities	394	112	730	683
Reclassification adjustment for net gain on sale of available for sale securities, included in net income	(78)	(42)	(8,281)	(714)
Derivatives:
Change in net unrealized loss on effective cash flow hedge interest rate swap derivatives	(197)	(2,619)	(25,236)	(11,392)
Reclassification adjustment of net loss (gain) related to derivatives designated as cash flow hedges	1,587	(499)	2,283	(1,809)
Pension plans:
Amortization of net actuarial loss and prior service credit, included in net periodic benefit cost	819	595	2,207	1,784
Prior service cost adjustment due to plan amendment	0	0	163	0
Change in net actuarial loss	0	0	(7,558)	0
Other comprehensive income, before tax	4,126	14,881	53,208	84,708
Income tax expense related to items of other comprehensive income	(866)	(3,125)	(11,173)	(17,789)
Other comprehensive income, net of tax	3,260	11,756	42,035	66,919
Comprehensive income	$ 30,334	$ 31,548	$ 94,616	$ 124,138