Stock-Based Compensation, Restricted Shares (Details) - Restricted Shares - 2012 Directors Restricted Stock Plan - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2021	Dec. 31, 2020
Stock-Based Compensation
Remaining shares available for the granting of stock options under plan	143,196		143,196
Restricted share activity
Restricted shares outstanding at the beginning of the period (in shares)	26,350	26,350	26,350
Shares vested and issued (in shares)	(27,272)
Restricted shares granted (in shares)	20,146	0
Restricted shares outstanding at the end of the period (in shares)	19,224	26,350	19,224	26,350
Fair Value at Grant Date
Fair value at the grant date, restricted shares outstanding at the beginning of the period (in dollars per share)	$ 45.55	$ 45.55	$ 45.55
Fair value of restricted shares vested and issued (in dollars per share)	45.80
Fair value of restricted shares granted (in dollars per share)	65.96	0
Fair value at the grant date, restricted shares outstanding at the end of the period (in dollars per share)	$ 66.59	$ 45.55	$ 66.59	$ 45.55
Weighted Average Remaining Amortization Term (in years)	10 months 17 days	1 month 17 days		4 months 17 days
Total compensation cost related to non-vested restricted shares not yet recognized (in dollars)	$ 1.1		$ 1.1
Weighted average expected amortization period			10 months 17 days