Incentive Plans - Changes in Stock Options Outstanding (Details) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Shares
Exercised (in shares)	(32,554)	(11,359)	(12,345)
Outstanding at end of year (in shares)	1,319,500
Exercisable at end of year (in shares)	1,319,500
Stock Options
Number of Shares
Outstanding at beginning of year (in shares)	2,048,400	2,920,410	3,994,595
Exercised (in shares)	(170,000)	(47,000)	(57,500)
Forfeited (in shares)	(558,900)	(825,010)	(1,016,685)
Outstanding at end of year (in shares)	1,319,500	2,048,400	2,920,410
Exercisable at end of year (in shares)	1,319,500	2,048,400	2,694,410	3,182,345
Average Exercise Price
Outstanding at beginning of year (in USD per share)	$ 40.14	$ 43.93	$ 44.66
Exercised (in USD per share)	17.57	17.57	17.57
Forfeited (in USD per share)	52.61	54.85	48.29
Outstanding at end of year (in USD per share)	37.77	40.14	43.93
Exercisable at end of year (in USD per share)	$ 34.25	$ 37.88	$ 43.51	$ 49.10