Employee Benefit Plans - Changes in Projected Benefit Obligation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
DB Pension Plans
Change in benefit obligation:
Benefit obligation at beginning of year	$ 82,748	$ 77,304
Service cost	0	0	$ 0
Interest cost	2,508	2,501	2,473
Plan participants’ contributions	0	0
Amendments	0	0
Curtailments	0	0
Actuarial loss (gain)	(2,324)	5,928
Benefits paid	(3,243)	(2,985)
Benefit obligation at end of year	79,689	82,748	77,304
Change in plan assets:
Fair value of plan assets at beginning of year	80,154	71,807
Actual return on plan assets	(4,437)	9,582
Plan participants’ contributions	0	0
Employer contributions	0	1,750
Benefits paid	(3,243)	(2,985)
Fair value of plan assets at end of year	72,474	80,154	71,807
Unfunded status	(7,215)	(2,594)
Life and Healthcare Plan
Change in benefit obligation:
Benefit obligation at beginning of year	8,995	9,121
Service cost	212	192	258
Interest cost	270	268	283
Plan participants’ contributions	122	98
Amendments	0	(964)
Curtailments	0	0
Actuarial loss (gain)	(1,337)	708
Benefits paid	(405)	(428)
Benefit obligation at end of year	7,857	8,995	9,121
Change in plan assets:
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Plan participants’ contributions	122	98
Employer contributions	283	330
Benefits paid	(405)	(428)
Fair value of plan assets at end of year	0	0	0
Unfunded status	(7,857)	(8,995)
SERP Plan
Change in benefit obligation:
Benefit obligation at beginning of year	26,142	23,399
Service cost	160	166	171
Interest cost	833	852	832
Plan participants’ contributions	0	0
Amendments	0	0
Curtailments	0	0
Actuarial loss (gain)	(2,987)	2,407
Benefits paid	(609)	(682)
Benefit obligation at end of year	23,539	26,142	23,399
Change in plan assets:
Fair value of plan assets at beginning of year	0	0
Actual return on plan assets	0	0
Plan participants’ contributions	0	0
Employer contributions	609	682
Benefits paid	(609)	(682)
Fair value of plan assets at end of year	0	0	$ 0
Unfunded status	$ (23,539)	$ (26,142)