Stockholders' Equity (ATM Program) (Details) - USD ($)		1 Months Ended	3 Months Ended
		Oct. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Class of Stock [Line Items]
Total allowable shares (in shares)			375,000,000		375,000,000
Total shares issued (in shares)			175,810,465		175,635,792
Net proceeds			$ 748,000	$ 1,882,000
Stock issuance costs			$ 48,000	$ 5,145,000
Series F Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares redeemed (in shares)		13,800,000
Dividend rate		5.20%
Stated liquidation value per share (in dollars per share)		$ 25.00
Aggregate redemption price (in dollars per share)		$ 25.111944
Excess of redemption value over carrying value of preferred shares redeemed		$ 10,897,000
ATM equity programs
Class of Stock [Line Items]
Shares of common stock (in shares)				30,000
Average price per share (net) (in dollars per share)				$ 38.59
Net proceeds				$ 1,158,000
Stock issuance costs	[1]			$ 75,000
2020 ATM
Class of Stock [Line Items]
Total allowable shares (in shares)			17,500,000
Total shares issued (in shares)			1,599,304

[1] Stock issuance costs consist primarily of underwriters' fees and commissions, and legal and accounting fees.