Pension Plans - SERP (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SERP
Defined contribution plan
Expenses recorded	$ 120,000	$ 112,000	$ 80,000
Employer contributions	108,000	85,000	96,000
Liability for pension benefits	120,000	108,000
401(k) plan
Defined contribution plan
Expenses recorded	$ 118,000	$ 129,000	$ 123,000