Common Stock (Details) - USD ($)	3 Months Ended	9 Months Ended		12 Months Ended		17 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	May 08, 2019
Class of Stock [Line Items]
Net proceeds		$ 90,635,000	$ 129,341,000	$ 119,240,000	$ 391,509,000
Restricted Stock/Unit Plan, and Management Incentive Plan
Class of Stock [Line Items]
Common stock issued (in shares)		96,000
Dividend Reinvestment and Stock Purchase Plan
Class of Stock [Line Items]
Common stock issued (in shares)		130,000
Common stock issued, amount		$ 9,000,000
Equity Shelf Program
Class of Stock [Line Items]
Sale of stock, maximum amount of stock allowed to be offered							$ 300,000,000
Gross proceeds	$ 32,788,633					$ 207,125,867
Less: agent commissions	(327,886)					(2,071,259)
Net proceeds	$ 32,460,747					$ 205,054,608
Number of shares sold (in shares)	506,219					2,705,376
Weighted average price per share	$ 64.77					$ 76.56
Sale of common stock available for sale (in shares)	$ 92,874,133	$ 92,874,133		$ 92,874,133		$ 92,874,133