Employee Benefits (Retirement Plans And Other Postretirement Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,129	$ 2,191	$ 6,388	$ 6,001	$ 8,388	$ 8,199
Interest cost	3,264	3,250	9,794	9,780	13,053	13,403
Expected return on plan assets	(4,797)	(4,734)	(14,392)	(14,159)	(19,112)	(19,108)
Amortization of net (gain) loss	2,114	1,730	6,341	5,505	8,175	8,167
Amortization of prior service benefit	(877)	(875)	(2,630)	(2,630)	(3,506)	(3,506)
Net periodic benefit cost (benefit)	1,833	1,562	5,501	4,497	6,998	7,155
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	559	749	1,677	2,179	2,267	3,042
Interest cost	680	871	2,042	2,616	2,593	3,625
Expected return on plan assets	(477)	(452)	(1,430)	(1,372)	(1,893)	(1,889)
Amortization of net (gain) loss	(419)	(643)	(1,258)	(1,973)	(1,659)	(2,479)
Amortization of prior service benefit	(1,537)	(788)	(4,613)	(2,363)	(6,151)	(3,130)
Net periodic benefit cost (benefit)	$ (1,194)	$ (263)	$ (3,582)	$ (913)	$ (4,843)	$ (831)