CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 74,554	$ 74,138	$ 54,312
Securities available for sale and transferred securities:
Change in unrealized holding gain (loss) on available for sale securities during the period	87,481	(34,238)	15,217
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12	0	11,881	0
Change in net unrealized loss on securities transferred from held to maturity to available for sale	0	401	0
Reclassification adjustment for amortization related to available for sale and held to maturity debt securities	816	1,244	1,255
Reclassification adjustment for net (gain) loss on sale of available for sale securities, included in net income	(756)	1,839	(625)
Derivatives:
Change in net unrealized (loss) gain on effective cash flow hedge interest rate swap derivatives	(9,118)	2,351	3
Change in net unrealized gains on interest rate swap derivatives terminated during the period	0	0	273
Reclassification adjustment of net (gain) loss related to derivatives designated as cash flow hedges	(2,043)	(1,406)	754
Pension plans:
Amortization of net actuarial loss and prior service credit, included in net periodic benefit cost	2,378	2,182	1,605
Effect of settlement recognition	0	0	8
Change in net actuarial loss	(9,816)	(1,994)	(5,218)
Other comprehensive income (loss), before tax	68,942	(17,740)	13,272
Income tax (expense) benefit related to items of other comprehensive income (loss)	(14,478)	3,725	(5,374)
Other comprehensive income (loss), net of tax	54,464	(14,015)	7,898
Comprehensive income	$ 129,018	$ 60,123	$ 62,210