Stockholders' Equity (Stock Transactions - Narrative) (Details)					3 Months Ended		6 Months Ended
	Aug. 03, 2021 $ / shares	Jun. 21, 2021 shares	May 11, 2021 USD ($) director shares	Feb. 10, 2021 USD ($) executiveOfficer shares	Jun. 30, 2021 USD ($) shares	Jun. 30, 2020 shares	Jun. 30, 2021 USD ($) $ / shares shares	Jun. 30, 2020 shares	Jul. 31, 2022 USD ($) shares	Aug. 04, 2021 USD ($)	Jul. 31, 2021 shares	Mar. 31, 2021 shares	Jan. 01, 2021 USD ($)	Dec. 31, 2020 shares
Class of Stock [Line Items]
Dividends declared per common share, during the period (in dollars per share) | $ / shares							$ 0.6050
Dilutive effect of forward equity shares (in shares)					61,064	0	27,896	2,149
Weighted-average incremental shares of common stock excluded from the computation (in shares)					0		0
Salary Deferral Plan | Non-vested Stock Award
Class of Stock [Line Items]
Shares issued though the salary deferral program during period, grant-date fair value | $													$ 600,000
Shares issued during the period (in shares)							21,396
Executive Incentive Program | Non-vested Stock Award
Class of Stock [Line Items]
Granted (in dollars per share) | $				$ 3,800,000
Granted (in shares)				124,648
Award vesting period				5 years
Executive Incentive Program | Executive Officer | Non-vested Stock Award
Class of Stock [Line Items]
Number of executive officers granted awards | executiveOfficer				4
Executive Incentive Program | Senior Vice President | Non-vested Stock Award
Class of Stock [Line Items]
Number of executive officers granted awards | executiveOfficer				5
Executive Incentive Program | First Vice President | Non-vested Stock Award
Class of Stock [Line Items]
Number of executive officers granted awards | executiveOfficer				5
Stock incentive plan
Class of Stock [Line Items]
Granted (in shares)					37,978	39,493	203,701	78,837
Stock incentive plan | Performance Shares
Class of Stock [Line Items]
Shares issued during the period (in shares)				19,679
Value of performance based awards released | $				$ 600,000
Stock incentive plan | Executive Officer | Performance Shares
Class of Stock [Line Items]
Number of executive officers excluded from award grant | executiveOfficer				4
Stock incentive plan | Senior Vice President | Performance Shares
Class of Stock [Line Items]
Number of executive officers excluded from award grant | executiveOfficer				5
Stock incentive plan | First Vice President | Performance Shares
Class of Stock [Line Items]
Number of executive officers excluded from award grant | executiveOfficer				5
Stock incentive plan | Directors | Non-vested Stock Award
Class of Stock [Line Items]
Shares issued though the salary deferral program during period, grant-date fair value | $			$ 1,200,000
Shares issued during the period (in shares)			36,682
Award vesting period			1 year
Number of directors | director			8
Stock incentive plan | Employee | Non-vested Stock Award
Class of Stock [Line Items]
Shares issued during the period (in shares)		1,296
Subsequent event
Class of Stock [Line Items]
At-the-market equity offering program, remaining authorized amount, assuming forward equity contracts settle | $										$ 58,200,000
Dividends declared per common share, during the period (in dollars per share) | $ / shares	$ 0.3025
Forecast
Class of Stock [Line Items]
Shares sold of a forward basis, remaining expected proceeds | $									$ 114,800,000
At the market equity offering program
Class of Stock [Line Items]
At-the-market equity offering program, authorized amount | $					$ 500,000,000.0		$ 500,000,000.0
Shares sold on a forward basis remaining to be settled (in shares)					2,007,429		2,007,429					0		1,823,259
Shares included in forward equity sales agreement (in shares)					5,800,000
Dilutive effect of forward equity shares (in shares)					2,000,000.0		2,000,000.0
At the market equity offering program | Subsequent event
Class of Stock [Line Items]
Shares sold on a forward basis remaining to be settled (in shares)											3,677,615
At the market equity offering program | Forecast
Class of Stock [Line Items]
Shares sold on a forward basis remaining to be settled (in shares)									3,700,000