Pension, Savings, and Other Employee Benefits - Schedule Of Components Of Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits
Components of net periodic benefit cost
Service cost	$ 11	$ 9	$ 31	$ 28
Interest cost	6,935	7,276	20,908	22,035
Expected return on plan assets	(8,222)	(9,230)	(24,673)	(27,011)
Amortization of unrecognized:
Prior service cost/(credit)	0	13	0	39
Actuarial (gain)/loss	3,164	2,380	9,076	7,140
Net periodic benefit cost/(credit)	1,888	448	5,342	2,231
Other Benefits
Components of net periodic benefit cost
Service cost	33	26	100	80
Interest cost	328	328	982	979
Expected return on plan assets	(268)	(236)	(806)	(710)
Amortization of unrecognized:
Prior service cost/(credit)	0	23	0	71
Actuarial (gain)/loss	(108)	(140)	(290)	(425)
Net periodic benefit cost/(credit)	$ (15)	$ 1	$ (14)	$ (5)