Stockholders' Equity (ATM Program) (Details) - USD ($) $ / shares in Units, $ in Thousands		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Class of Stock [Line Items]
Total allowable shares (in shares)		375,000,000		375,000,000
Total shares issued (in shares)		175,616,386		175,232,971
Net proceeds		$ 3,325	$ 65,440
Stock issuance costs		$ 17,125	$ 7,810
ATM equity programs
Class of Stock [Line Items]
Shares of common stock (in shares)		30,000	1,634,350
Average price per share (net) (in dollars per share)		$ 35.35	$ 36.56
Net proceeds		$ 1,061	$ 59,752
Stock issuance costs	[1]	$ 173	$ 1,151
2020 ATM
Class of Stock [Line Items]
Total allowable shares (in shares)		17,500,000
Total shares issued (in shares)		1,599,304
2018 ATM
Class of Stock [Line Items]
Total allowable shares (in shares)		12,000,000
Total shares issued (in shares)		11,272,034

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