Supplemental Executive Retirement Plans - Plan Details and Change in Benefit Obligation (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) payment	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($)
Retirement Benefits [Abstract]
Number of annual payments | payment			15
Change in Benefit Obligation
Benefit obligation at the beginning of the period	$ 18,278	$ 17,763	$ 19,746	$ 19,214
Service cost	123	98	370	294
Interest cost	87	121	261	363
Payments	(12)	(12)	(1,901)	(1,901)
Benefit obligation at the end of the period	18,476	$ 17,970	18,476	$ 17,970
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	16,563		16,563		17,833
Total accrued liabilities	$ 18,476		$ 18,476		$ 19,746