CONDENSED CONSOLIDATED STATEMENTS OF EQUITY (Parenthetical) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Dividends declared and paid:
Common stock dividends (in dollars per share)	$ 0.50	$ 0.475	$ 1.000	$ 0.950
Issuance of common stock:
Director compensation (in shares)	6,962	13,036	14,969	22,633
Stock purchase plan (in shares)	1,832	2,969	4,156	5,506
ATM equity program (in shares)	1,495,548	3,037,464	1,495,548	3,037,464
Issuance of restricted common stock (in shares)			259,650	222,684
Series E Preferred Stock
Dividends declared and paid:
Preferred stock dividends (in dollars per share)	$ 0.356250	$ 0.356250	$ 0.712500	$ 0.712500
Series F Preferred Stock
Dividends declared and paid:
Preferred stock dividends (in dollars per share)	$ 0.32500	$ 0.32500	$ 0.650000	$ 0.650000