Employee Benefits (Retirement Plans And Other Postretirement Benefits) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Retirement Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 2,757	$ 1,989	$ 5,515	$ 4,259	$ 9,774	$ 8,450
Interest cost	3,222	3,282	6,445	6,530	12,974	13,039
Expected return on plan assets	(5,315)	(4,787)	(10,630)	(9,595)	(20,224)	(19,049)
Amortization of net (gain) loss	2,100	2,138	4,200	4,227	8,427	7,791
Amortization of prior service benefit	(877)	(875)	(1,755)	(1,753)	(3,508)	(3,504)
Net periodic benefit cost (benefit)	1,887	1,747	3,775	3,668	7,443	6,727
Other Postretirement Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Service cost	700	530	1,400	1,118	2,518	2,457
Interest cost	565	684	1,130	1,362	2,491	2,784
Expected return on plan assets	(612)	(483)	(1,225)	(953)	(2,179)	(1,868)
Amortization of net (gain) loss	(525)	(444)	(1,050)	(839)	(1,889)	(1,883)
Amortization of prior service benefit	(1,537)	(1,538)	(3,075)	(3,076)	(6,150)	(5,402)
Net periodic benefit cost (benefit)	$ (1,409)	$ (1,251)	$ (2,820)	$ (2,388)	$ (5,209)	$ (3,912)