Supplemental Executive Retirement Plans - Plan Details and Change in Benefit Obligation (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) payment	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Supplemental Executive Retirement Plans
Number of annual payments | payment			15
Change in Benefit Obligation
Benefit obligation at the beginning of the period	$ 17,763	$ 17,535	$ 19,214	$ 18,927
Service cost	98	84	294	251
Interest cost	121	164	363	494
Payments	(12)	(12)	(1,901)	(1,901)
Benefit obligation at the end of the period	17,970	$ 17,771	17,970	$ 17,771
Amounts Recognized in the Condensed Consolidated Balance Sheets:
Current accrued expenses and other current liabilities	1,913		1,913		$ 1,913
Non-current other liabilities	16,057		16,057		17,301
Total accrued liabilities	$ 17,970		$ 17,970		$ 19,214