Postretirement Benefits - Pension Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Fair value of plan assets:
Fair value of plan assets, beginning of year	$ 1,081,061	$ 907,625
Actual gain on plan assets	86,966	195,713
Employer contributions	1,245	1,571
Benefits paid	(29,029)	(23,848)
Fair value of plan assets, end of year	$ 1,140,243	$ 1,081,061