Stockholders' Equity (Stock Rollforward) (Details) - shares	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Increase (Decrease) in Stock by Class [Roll Forward]
Common stock, beginning of period	21,193,402
Treasury stock, beginning of period	1,686,046
Changes related to deferred compensation plan for Boards of Directors:
Common shares issued under compensation plan for Boards of Directors	(4,347)	(3,680)
Common stock, end of period	21,208,689
Treasury stock, end of period	1,605,492
Common Shares
Increase (Decrease) in Stock by Class [Roll Forward]
Common stock, beginning of period	21,193,402
Changes related to stock-based compensation awards:
Cancellation of restricted common shares	0
Changes related to deferred compensation plan for Boards of Directors:
Common shares issued under dividend reinvestment plan	15,287
Common stock, end of period	21,208,689
Treasury Stock
Increase (Decrease) in Stock by Class [Roll Forward]
Treasury stock, beginning of period	1,686,046
Changes related to stock-based compensation awards:
Release of restricted common shares	27,772
Cancellation of restricted common shares	4,607
Grant of common shares	(4,897)
Changes related to deferred compensation plan for Boards of Directors:
Purchase of treasury stock	4,040
Disbursed out of treasury stock	(2,983)
Common shares issued under compensation plan for Boards of Directors	(3,643)
Common shares issued under employee stock purchase plan	7,509
Treasury stock, end of period	1,605,492
Restricted Shares | Treasury Stock
Changes related to stock-based compensation awards:
Grant of common shares	(97,941)