Employee Benefit Plans - Fair Value Hierarchy (Details) - Post-Retirement Medical Benefits - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Employee benefit plans
Fair value of post-retirement plan assets	$ 11,240	$ 13,773	$ 12,313
Fair Value
Employee benefit plans
Fair value of post-retirement plan assets	11,240	13,773
Level 1
Employee benefit plans
Fair value of post-retirement plan assets	11,240	13,773
Level 2
Employee benefit plans
Fair value of post-retirement plan assets	0	0
Level 3
Employee benefit plans
Fair value of post-retirement plan assets	0	0
Cash equivalents | Fair Value
Employee benefit plans
Fair value of post-retirement plan assets	215	92
Cash equivalents | Level 1
Employee benefit plans
Fair value of post-retirement plan assets	215	92
Cash equivalents | Level 2
Employee benefit plans
Fair value of post-retirement plan assets	0	0
Cash equivalents | Level 3
Employee benefit plans
Fair value of post-retirement plan assets	0	0
Fixed income fund | Fair Value
Employee benefit plans
Fair value of post-retirement plan assets	4,380	5,409
Fixed income fund | Level 1
Employee benefit plans
Fair value of post-retirement plan assets	4,380	5,409
Fixed income fund | Level 2
Employee benefit plans
Fair value of post-retirement plan assets	0	0
Fixed income fund | Level 3
Employee benefit plans
Fair value of post-retirement plan assets	0	0
U.S. equity securities | Fair Value
Employee benefit plans
Fair value of post-retirement plan assets	6,645	8,272
U.S. equity securities | Level 1
Employee benefit plans
Fair value of post-retirement plan assets	6,645	$ 8,272
U.S. equity securities | Level 2
Employee benefit plans
Fair value of post-retirement plan assets	0
U.S. equity securities | Level 3
Employee benefit plans
Fair value of post-retirement plan assets	$ 0