Employee Benefit Plans 8 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Post-Retirement Medical Benefits
Employee benefit plans
Employer contributions	$ 242	$ 269
Pension Benefits
Employee benefit plans
Employer contributions	3,489	$ 3,718
Expected future employer's contribution	$ 3,100
Minimum | Fixed income fund | Post-Retirement Medical Benefits
Employee benefit plans
Maturity period of investments	1 year
Maximum | Fixed income fund | Post-Retirement Medical Benefits
Employee benefit plans
Maturity period of investments	20 years