Stock-Based Compensation, Restricted Shares (Details) - Restricted Shares - 2012 Directors Restricted Stock Plan - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Stock-Based Compensation
Shares available for the granting of additional stock options	163,342
Restricted share activity
Restricted shares outstanding at the beginning of the period (in shares)	26,350
Restricted shares granted (in shares)	0
Restricted shares outstanding at the end of the period (in shares)	26,350	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
Fair value of restricted shares granted (in dollars per share)	0
Fair value at the grant date, restricted shares outstanding at the end of the period (in dollars per share)	$ 45.55	$ 45.55
Weighted Average Remaining Amortization Term (in years)	1 month 17 days	4 months 17 days
Total compensation cost related to non-vested restricted shares not yet recognized (in dollars)	$ 0.2
Weighted average expected amortization period	1 month 17 days