Pension and Other Retirement Plans - Components of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 934	$ 768	$ 692
Interest cost	71,138	78,195	82,724
Expected return on plans’ assets	(99,283)	(101,126)	(107,616)
Recognized actuarial loss	17	0	0
Amortization of prior service costs (credits)	140	116	90
Net periodic benefit credit	(27,054)	(22,047)	(24,110)
Other Postretirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	0	0
Interest cost	230	264	320
Expected return on plans’ assets	0	0	0
Recognized actuarial loss	0	0	0
Amortization of prior service costs (credits)	(381)	(380)	(380)
Net periodic benefit credit	$ (151)	$ (116)	$ (60)