Qualified Employee Benefit Plans - Valuation of our Retirement Plan Assets by Pricing Observability Levels (Details) - Retirement Plan - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	$ 130,939	$ 125,022	$ 114,080
Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	108,466	103,287
Level 1
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	76,111	76,688
Level 2
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	32,355	26,599
Level 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
NAV Expedient
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	22,473	21,735
Cash | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	47	458
Cash | Level 1
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	47	458
Cash | Level 2
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Cash | Level 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
U.S. Treasury Strips | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	32,355	26,599
U.S. Treasury Strips | Level 1
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
U.S. Treasury Strips | Level 2
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	32,355	26,599
U.S. Treasury Strips | Level 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Fixed income mutual funds | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	17,477	17,834
Fixed income mutual funds | Level 1
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	17,477	17,834
Fixed income mutual funds | Level 2
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value		0
Fixed income mutual funds | Level 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Equity mutual funds | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	43,786	44,020
Equity mutual funds | Level 1
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	43,786	44,020
Equity mutual funds | Level 2
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value		0
Equity mutual funds | Level 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Equity securities | Fair Value, Inputs, Level 1, 2 and 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	14,801	14,376
Equity securities | Level 1
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	14,801	14,376
Equity securities | Level 2
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Equity securities | Level 3
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	$ 0	$ 0