Employee Benefits (Retirement Plans And Other Postretirement Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,488	$ 2,758	$ 10,818	$ 9,006
Interest cost	3,608	3,223	13,263	13,034
Expected return on plan assets	(5,383)	(5,315)	(21,144)	(19,696)
Amortization of net (gain) loss	1,418	2,100	7,871	8,465
Amortization of prior service benefit	(878)	(878)	(3,506)	(3,506)
Net periodic benefit cost (benefit)	1,253	1,888	7,302	7,303
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	625	700	2,720	2,348
Interest cost	618	565	2,305	2,610
Expected return on plan assets	(530)	(613)	(2,352)	(2,050)
Amortization of net (gain) loss	(575)	(525)	(2,216)	(1,808)
Amortization of prior service benefit	(1,308)	(1,538)	(5,921)	(6,151)
Net periodic benefit cost (benefit)	$ (1,170)	$ (1,411)	$ (5,464)	$ (5,051)