Shareholders' Equity, Stock Repurchase Program, Dividends and Issuance of Common Stock (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended	12 Months Ended
	Aug. 05, 2008	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 23, 2020	Feb. 18, 2016
Stock Repurchased [Abstract]
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01	$ 0.01
Stock Issued [Abstract]
Per share price of shares issued (in dollars per share)		$ 770.00	$ 770.00
Minimum [Member]
Stock Issued [Abstract]
Per share price of shares issued (in dollars per share)				715.00	$ 635.00
Maximum [Member]
Stock Issued [Abstract]
Per share price of shares issued (in dollars per share)				$ 770.00	$ 690.00
Directors and Officers [Member]
Stock Issued [Abstract]
Issuance of Common Stock (in shares)					2,400
Non-qualified Deferred Compensation Retirement Plans [Member]
Stock Issued [Abstract]
Issuance of common stock (in shares)			523	9,312	13,520
1998 Common Stock Repurchase Plan [Member]
Stock Repurchased [Abstract]
Approved funds available for common stock repurchase program		$ 20.0	$ 20.0
Number of shares of stock purchased (in shares)			0	0
2020 Common Stock Repurchase Plan [Member]
Stock Repurchased [Abstract]
Shares repurchased from shareholders		$ 2.8
2020 Common Stock Repurchase Plan [Member] | Maximum [Member]
Stock Repurchased [Abstract]
Approved funds available for common stock repurchase program						$ 8.5
Share Purchase Rights Plan [Member]
Stock Repurchased [Abstract]
Number of preferred stock purchase rights declared as dividend for each share of common stock (in shares)	1
Common stock, par value (in dollars per share)	$ 0.01
Dividend, declared date			Aug. 05, 2008
Dividend, record date			Aug. 15, 2008
Threshold percentage of beneficial ownership or tender offer of Acquiring Person for triggering exercise of rights	10.00%
Number of shares of preferred stock which the registered holder of each right is entitled to purchase (in shares)							0.01
Redeemable price for a right issue (in dollars per share)		$ 0.001	$ 0.001
Market value of common stock shares as multiple of exercise price of right	2
Term of extension of expiration date	7 years
Stock Issued [Abstract]
Per share price of shares issued (in dollars per share)		$ 1,600	$ 1,600				$ 1,200
Share Purchase Rights Plan [Member] | Series A Junior Participating Preferred Stock [Member]
Stock Repurchased [Abstract]
Number of shares of preferred stock which the registered holder of each right is entitled to purchase (in shares)		0.01	0.01
Preferred stock, par value (in dollars per share)		$ 0	$ 0
Stock Issued [Abstract]
Per share price of shares issued (in dollars per share)	$ 1,600