Condensed Consolidated Statements of Stockholders' Equity (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Exercise of stock options	14,609	186,521
Common stock purchase plan	58,734	44,161
Purchase of treasury stock	110,520	111,835
Common stock dividends/distributions	$ 1.00	$ 0.96
Preferred stock dividend shares	$ 15.95	$ 15.95
Additional Paid-in Capital [Member]
Exercise of stock options	14,609	186,521
Common stock purchase plan	58,734	44,161
Treasury Stock [Member]
Purchase of treasury stock	110,520	111,835
Accumulated Deficit [Member]
Common stock dividends/distributions	$ 1.00	$ 0.96
Preferred stock dividend shares	$ 15.95	$ 15.95