CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stockholders' Equity Attributable to Parent
Common dividends declared - per share (in dollars per share)	$ 3.08	$ 2.94	$ 2.72
Issuance of shares of common stock, common stock offering, net of expenses (in shares)	709,924	2,388,342	1,706,474
Issuance of shares of common stock, options exercised (in shares)	0	0	0
Issuance of shares of common stock, dividend reinvestment plan (in shares)	0	1,893	1,844
Withheld shares of common stock to satisfy tax withholding obligations in connection with the vesting of restricted stock (in shares)	36,445	28,955	23,824