Employee Benefit Plans - Schedule of beginning and ending balances of accumulated postretirement benefit obligations (Details) - Other Postretirement Benefit Plans, Defined Benefit - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Accumulated postretirement benefit obligations at the beginning of the year	$ 2,126,000	$ 1,730,000
Service Cost	38,000	30,000
Interest Cost	70,000	71,000
Actuarial loss	357,000	390,000
Benefits paid	(62,000)	(95,000)
Accumulated postretirement benefit obligations at the end of the year	$ 2,529,000	$ 2,126,000