Retirement Plans, Summary of Change in Plan Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Pension Plan [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	$ 294,995	$ 257,517
Actual return on plan assets	(18,214)	45,196
Employer contribution	8,102	0
Gross benefits paid	(11,749)	(7,718)
Acquisition	30,017	0
Fair value of plan assets at end of year	303,151	294,995
SERP [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contribution	145	145
Gross benefits paid	(145)	(145)
Acquisition	0	0
Fair value of plan assets at end of year	0	0
Other Postretirement Benefits [Member]
Change in plan assets [Roll Forward]
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Employer contribution	103	75
Gross benefits paid	(103)	(75)
Acquisition	0	0
Fair value of plan assets at end of year	$ 0	$ 0