Employee Benefit Plans - Other Compensation Plans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Classification of liabilities in the Consolidated Balance Sheets
Unfunded liability	$ 5,121	$ 4,793
Current liabilities	1,218	1,040
Other long-term liabilities	3,903	3,753
Total liabilities	5,121	4,793
Plan expenses	1,200	1,200	$ 1,300
Accrued compensation
Classification of liabilities in the Consolidated Balance Sheets
Current liabilities	$ 1,218	$ 1,040