Retirement Plans, Schedule of Change in Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Plan [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	$ 381,483	$ 354,994
Service cost	7,364	7,622	$ 10,677
Interest cost	16,493	15,499	13,729
Actuarial loss (gain)	49,478	(44,935)
Gross benefits paid	(11,957)	(11,749)
Curtailments	0	(3,081)
Acquisition	0	63,133
Benefit obligation at end of year	442,861	381,483	354,994
Accumulated benefit obligation at end of year	417,981	356,797
SERP [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	1,246	1,412
Service cost	0	0	0
Interest cost	52	49	58
Actuarial loss (gain)	72	(70)
Gross benefits paid	(145)	(145)
Curtailments	0	0
Acquisition	0	0
Benefit obligation at end of year	1,225	1,246	1,412
Accumulated benefit obligation at end of year	1,225	1,246
Other Postretirement Benefits [Member]
Change in benefit obligation [Roll Forward]
Benefit obligation at beginning of year	743	679
Service cost	0	0	0
Interest cost	31	24	27
Actuarial loss (gain)	(22)	143
Gross benefits paid	(90)	(103)
Curtailments	0	0
Acquisition	0	0
Benefit obligation at end of year	662	743	$ 679
Accumulated benefit obligation at end of year	$ 662	$ 743