CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 19,792	$ 20,303	$ 57,219	$ 56,757
Securities available for sale and transferred securities:
Change in unrealized holding gain (loss) on available for sale securities during the period	17,334	(16,885)	96,156	(65,039)
Unrealized net gain on securities transferred from held to maturity to available for sale under the transition guidance enumerated in ASU 2017-12	0	0	0	11,881
Change in net unrealized loss on securities transferred from held to maturity to available for sale	0	0	0	401
Reclassification adjustment for amortization (accretion) related to available for sale and held to maturity debt securities	112	(661)	683	729
Reclassification adjustment for net (gain) loss on sale of available for sale securities, included in net income	(42)	741	(714)	1,900
Derivatives:
Change in net unrealized (loss) gain on effective cash flow hedge interest rate swap derivatives	(2,619)	1,894	(11,392)	7,864
Reclassification adjustment of net gain related to derivatives designated as cash flow hedges	(499)	(406)	(1,809)	(864)
Pension plans:
Amortization of net actuarial loss and prior service credit, included in net periodic benefit cost	595	546	1,784	1,637
Other comprehensive income (loss), before tax	14,881	(14,771)	84,708	(41,491)
Income tax (expense) benefit related to items of other comprehensive income (loss)	(3,125)	3,102	(17,789)	8,713
Other comprehensive income (loss), net of tax	11,756	(11,669)	66,919	(32,778)
Comprehensive income	$ 31,548	$ 8,634	$ 124,138	$ 23,979