Pension Plans - SERP (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SERP
Defined contribution plan
Expenses recorded	$ 112,000	$ 80,000	$ 96,000
Employer contributions	85,000	96,000	81,000
Liability for pension benefits	108,000	81,000
401(k) plan
Defined contribution plan
Expenses recorded	$ 129,000	$ 123,000	$ 128,000