Pension Plan (Details) - Change in unrecognized pension costs recorded in other comprehensive loss - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension Plan (Details) - Change in unrecognized pension costs recorded in other comprehensive loss [Line Items]
Balance at beginning of year	$ 8,296,000	$ 7,954,000
Net actuarial loss	1,043,000	606,000
Recognized loss	(288,000)	(264,000)
Balance at end of year	$ 9,051,000	$ 8,296,000