Stock-Based Compensation Plans - Outstanding and Exercisable Options (Details)	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Exercise Price $38
Stock Option Plans
Weighted Average Exercise Price of Options Exercisable (in dollars per share)	$ 38
Options Outstanding and Exercisable (in shares) | shares	12,000
Options Outstanding and Exercisable, Weighted Average Remaining Contractual Life (In Years)	4 months 24 days
Options Outstanding and Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 38.00
Range of Exercise Price $44 - $45
Stock Option Plans
Range of exercise price, lower limit (in dollars per share)	44
Range of exercise price, upper limit (in dollars per share)	$ 45
Options Outstanding and Exercisable (in shares) | shares	14,000
Options Outstanding and Exercisable, Weighted Average Remaining Contractual Life (In Years)	1 year 4 months 24 days
Options Outstanding and Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 44.99
Range of Exercise Price $38 -$45
Stock Option Plans
Range of exercise price, lower limit (in dollars per share)	38
Range of exercise price, upper limit (in dollars per share)	$ 45
Options Outstanding and Exercisable (in shares) | shares	26,000
Options Outstanding and Exercisable, Weighted Average Remaining Contractual Life (In Years)	10 months 24 days
Options Outstanding and Exercisable, Weighted Average Exercise Price (in dollars per share)	$ 41.76