Employee Benefits (Retirement Plans And Other Postretirement Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,270	$ 1,905	$ 8,366	$ 8,597
Interest cost	3,248	3,265	13,022	14,135
Expected return on plan assets	(4,808)	(4,712)	(18,975)	(19,560)
Amortization of prior service benefit	(878)	(878)	(3,506)	(3,496)
Amortization of net (gain) loss	2,089	1,888	7,540	9,785
Net periodic benefit cost (benefit)	1,921	1,468	6,447	9,461
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	588	715	2,642	3,294
Interest cost	678	873	2,972	3,883
Expected return on plan assets	(470)	(460)	(1,845)	(2,005)
Amortization of prior service benefit	(1,538)	(788)	(4,651)	(3,081)
Amortization of net (gain) loss	(395)	(665)	(2,104)	(2,190)
Net periodic benefit cost (benefit)	$ (1,137)	$ (325)	$ (2,986)	$ (99)