Stock-based Employee Compensation, Stock Option Plans, and Deferred Compensation Plan for Directors - Summary of Option Activity (Details) - USD ($)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Number of Shares
Outstanding at beginning of period (in shares)	1,502,670
Granted (in shares)	250,500
Exercised (in shares)	(3,000)
Expired/Forfeited (in shares)	(87,000)
Outstanding at end of period (in shares)	1,663,170
Exercisable at end of period (in shares)	1,137,295
Weighted Average Exercise Price per share
Outstanding at beginning of period (in usd per share)	$ 52.86
Granted (in usd per share)	43.89
Exercised (in usd per share)	41.82
Expired/Forfeited (in usd per share)	53.60
Outstanding at end of period (in usd per share)	51.49
Exercisable at end of period (in usd per share)	$ 52.89
Aggregate Intrinsic Value
Outstanding at beginning of period	$ 0
Granted	0
Exercised	3,450	$ 85,268
Expired/Forfeited	0
Outstanding at end of period	171,250
Exercisable at end of period	$ 133,340