Employee Benefits (Retirement Plans And Other Postretirement Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,758	$ 2,270	$ 9,006	$ 8,366
Interest cost	3,223	3,248	13,034	13,022
Expected return on plan assets	(5,315)	(4,808)	(19,696)	(18,975)
Amortization of net (gain) loss	2,100	2,089	8,465	7,540
Amortization of prior service benefit	(878)	(878)	(3,506)	(3,506)
Net periodic benefit cost (benefit)	1,888	1,921	7,303	6,447
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	700	588	2,348	2,642
Interest cost	565	678	2,610	2,972
Expected return on plan assets	(613)	(470)	(2,050)	(1,845)
Amortization of net (gain) loss	(525)	(395)	(1,808)	(2,104)
Amortization of prior service benefit	(1,538)	(1,538)	(6,151)	(4,651)
Net periodic benefit cost (benefit)	$ (1,411)	$ (1,137)	$ (5,051)	$ (2,986)