Stockholders' Equity (Stock Transactions - Narrative) (Details)		1 Months Ended	3 Months Ended				9 Months Ended
	Nov. 03, 2020 $ / shares	Nov. 04, 2020 USD ($) $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Jun. 30, 2020 USD ($) $ / shares shares	Mar. 31, 2020 USD ($) $ / shares shares	Sep. 30, 2019 $ / shares shares	Sep. 30, 2020 USD ($) numberOfForwardEquityAgreements $ / shares shares	Sep. 30, 2019 USD ($) $ / shares shares	Feb. 14, 2020 USD ($) investment_bank
Class of Stock [Line Items]
At-the-market equity offering program, authorized amount | $									$ 500,000,000.0
Net proceeds from issuance of common stock | $							$ 40,296,000	$ 192,514,000
Proceeds from issuance of common stock, adjusted for costs to borrow | $			$ 72,700,000				$ 72,700,000
Dividends declared per common share, during the period (in dollars per share)			$ 0.30			$ 0.30	$ 0.90	$ 0.90
Dilutive effect of forward equity shares (in shares) | shares			0			0	0	0
Weighted-average incremental shares of common stock excluded from the computation (shares) | shares			137,757				51,133
At the market equity offering program
Class of Stock [Line Items]
Number of investment banks included in the program | investment_bank									6
Issuance of common stock (in shares) | shares				1,071,987	196,250		1,268,237
Net proceeds from issuance of common stock | $				$ 32,900,000	$ 7,000,000.0		$ 39,900,000
Number of forward equity agreements | numberOfForwardEquityAgreements							3
Forward equity agreement (in shares) | shares							3,600,000
Stock price, per share to be subsequently sold (in USD per share)			$ 31.30				$ 31.30
Dilutive effect of forward equity shares (in shares) | shares			2,300,000				2,300,000
Forward Equity Agreement Maturing June 2021
Class of Stock [Line Items]
Forward equity agreement (in shares) | shares				1,579,371
Stock price, per share to be subsequently sold (in USD per share)				$ 31.66
Forward Equity Agreement Maturing July 2021
Class of Stock [Line Items]
Forward equity agreement (in shares) | shares			764,472
Stock price, per share to be subsequently sold (in USD per share)			$ 31.84				$ 31.84
Subsequent event
Class of Stock [Line Items]
At-the-market equity offering program, remaining authorized amount, assuming forward equity contracts settle | $		$ 347,600,000
Dividends declared per common share, during the period (in dollars per share)	$ 0.30
Subsequent event | Forward Equity Agreement Maturing July 2021
Class of Stock [Line Items]
Forward equity agreement (in shares) | shares		1,235,129
Stock price, per share to be subsequently sold (in USD per share)		$ 30.52
Minimum | At the market equity offering program
Class of Stock [Line Items]
Shares issued during period, price per share (in dollars per share)				30.50	$ 33.00		30.50
Maximum | At the market equity offering program
Class of Stock [Line Items]
Shares issued during period, price per share (in dollars per share)				31.29	36.15		36.15
Weighted Average | At the market equity offering program
Class of Stock [Line Items]
Shares issued during period, price per share (in dollars per share)				$ 31.08	$ 36.09		$ 31.86