Employee Benefits (Changes in Funded Status of Plan - Other Postretirement Benefit Plans) (Details) - Other Postretirement Benefit Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Change in projected benefit obligation:
Benefit obligation at end of prior year	$ 60,862		$ 67,290
Service cost excluding expenses	2,242		2,591
Service cost	2,423	[1]	2,795	[1]	$ 2,236
Interest cost	2,456		2,252		2,723
Actuarial gain	889		(9,295)
Benefits paid from plan assets	(2,643)		(3,003)
Benefits paid from corporate assets	(176)		(141)
Retiree contributions	1,262		1,168
Benefit obligation at end of year	64,892		60,862		67,290
Change in plan assets:
Fair value of plan assets at end of prior year	36,287		40,873
Actual return (loss) on plan assets	6,636		(2,997)
Employer contribution	450		450
Benefits paid from plan assets	(2,643)		(3,003)
Retiree contributions	1,262		1,168
Administrative and investment expenses	(181)		(204)
Fair value of plan assets at end of year	41,811		36,287		$ 40,873
Funded status at end of year	$ (23,081)		$ (24,575)

[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.