Employee Benefits (Net Periodic Benefit Costs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Retirement Income Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 9,491	[1]	$ 10,608	[1]	$ 8,156
Interest cost	13,451		12,013		12,196
Expected return on plan assets	(21,492)		(21,076)		(19,189)
Amortization of:
Net loss	5,022		7,531		7,572
Prior service benefit	(3,467)		(3,467)		(3,467)
Net periodic benefit cost	3,005		5,609		5,268
Administrative and investment expenses	1,364		1,522
Other Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	415		480		362
Interest cost	1,003		865		863
Expected return on plan assets	0		0		0
Amortization of:
Net loss	770		1,022		882
Prior service benefit	(39)		(39)		(39)
Net periodic benefit cost	2,149		2,328		$ 2,068
Administrative and investment expenses	$ 0		$ 0

[1] (a) Service cost for the Retirement Plan for 2019 and 2018 includes expenses of $1.4 million and $1.5 million, respectively, for administrative and investment expenses paid from plan assets during the year.