Employee Benefits (Net Periodic Benefit Cost) (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 2,423	[1]	$ 2,795	[1]	$ 2,236
Interest cost	2,456		2,252		2,723
Expected return on plan assets	(2,120)		(2,435)		(1,907)
Amortization of:
Prior service benefit	(5,234)		(6,151)		(6,151)
Net gain	(2,377)		(2,166)		(1,678)
Net periodic benefit cost	(4,852)		(5,705)		$ (4,777)
Administrative and investment expenses	$ 181		$ 204

[1] (a) Service cost for 2019 and 2018 includes expenses of $181 and $204 thousand, respectively, for administrative and investment expenses paid from plan assets during the year.