Employee Benefit Plans, Changes in Benefit Obligation and Plan Assets (Details) - Defined Benefit Pension Plans Combined [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Employee Benefit Plans [Abstract]
Maximum period of eligible service	30 years
Change in Benefit Obligation [Abstract]
Pension benefit obligation, beginning of year	$ 41,511	$ 44,636
Service cost	849	1,015
Interest cost	1,645	1,515
Actuarial (gain) loss	5,241	(4,140)
Benefit payments	(1,716)	(1,515)
Pension benefit obligation, end of year	47,530	41,511
Change in Plan Assets [Abstract]
Fair value of plan assets, beginning of year	40,624	41,439
Actual return on plan assets	8,141	(1,600)
Employer contributions	2,300	2,300
Benefits paid	(1,716)	(1,515)
Fair value of plan assets, end of year	49,349	40,624
Funded Status of Plans at end of year	$ 1,819	$ (887)
Change in discount rate	(1.00%)	0.60%
Threshold for amortization of gains and losses	10.00%
Changes in Plan Assets and Benefit Obligations Recognized in Regulatory Assets [Abstract]
Net gain (loss) arising during the period	$ (167)	$ 252
Recognized net actuarial loss	(421)	(406)
Recognized prior service credit	13	13
Total changes in regulatory asset during the year	(575)	(141)
Amounts Recognized in Regulatory Assets that Have Not Yet Been Recognized as Components of Net Periodic Benefit Cost [Abstract]
Net loss	8,154	8,742
Prior service credit	(76)	(89)
Regulatory asset	$ 8,078	$ 8,653