Stock-Based Compensation, Restricted Shares (Details) - Restricted Shares - 2012 Directors Restricted Stock Plan - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			9 Months Ended	12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2019	Dec. 31, 2018
Stock-Based Compensation
Shares available for the granting of additional stock options	94,846			94,846
Restricted share activity
Restricted shares outstanding at the beginning of the period (in shares)	14,304	14,873	14,873	14,873
Shares vested and issued (in shares)		(14,873)
Restricted shares granted (in shares)	0	14,304	0
Restricted shares outstanding at the end of the period (in shares)	14,304	14,304	14,873	14,304	14,873
Fair Value at Grant Date
Fair value at the grant date, restricted shares outstanding at the beginning of the period (in dollars per share)	$ 89.49	$ 87.89	$ 87.89	$ 87.89
Fair value of restricted shares vested and issued (in dollars per share)		87.89
Fair value of restricted shares granted (in dollars per share)	0	89.49	0
Fair value at the grant date, restricted shares outstanding at the end of the period (in dollars per share)	$ 89.49	$ 89.49	$ 87.89	$ 89.49	$ 87.89
Weighted Average Remaining Amortization Term (in years)	7 months 20 days	10 months 20 days	1 month 20 days		4 months 20 days
Total compensation cost related to non-vested restricted shares not yet recognized (in dollars)	$ 0.8			$ 0.8
Weighted average expected amortization period				7 months 20 days