Pension and Other Retirement Plans - Defined Benefit Pension Plans and Other Post Retirement Plans Summarized Info (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligations, beginning of year	$ 2,056,876	$ 1,990,263
Service cost	934	768	$ 692
Interest cost	71,138	78,195	82,724
Plan amendments	224	601
Impact of Medicare Reform Act	0	0
Actuarial (gain) loss	(135,146)	94,092
Benefits paid	(108,630)	(107,043)
Projected benefit obligations, end of year	1,885,396	2,056,876	1,990,263
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plans’ assets, beginning of year	1,660,001	1,545,862
Actual return on plans’ assets	(101,797)	221,182
Employer contributions	55,500	0
Benefits paid	(108,630)	(107,043)
Fair value of plans’ assets, end of year	1,505,074	1,660,001	1,545,862
Under funded status of the plans	(380,322)	(396,875)
Other Postretirement Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligations, beginning of year	7,674	8,875
Service cost	0	0	0
Interest cost	230	264	320
Plan amendments	0	0
Impact of Medicare Reform Act	25	42
Actuarial (gain) loss	(498)	(593)
Benefits paid	(666)	(914)
Projected benefit obligations, end of year	6,765	7,674	8,875
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plans’ assets, beginning of year	0	0
Actual return on plans’ assets	0	0
Employer contributions	666	914
Benefits paid	(666)	(914)
Fair value of plans’ assets, end of year	0	0	$ 0
Under funded status of the plans	$ (6,765)	$ (7,674)