Subsequent Events (Details) - USD ($) $ in Thousands	Jan. 01, 2021	Nov. 03, 2020	Sep. 30, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Long-term Debt			$ 3,854,855	$ 3,102,830
Private Placement [Member] | covenant relief period [Member] | Unsecured Debt [Member]
Subsequent Event [Line Items]
Long-term Debt			$ 340,000
Long-term Debt, Spread Increase, Percentage			0.60%
Unsecured Revolving Variable Rate Credit Facility, Variable Rate, Due February 27, 2022 [Member] | Unsecured Debt [Member]
Subsequent Event [Line Items]
Debt Covenant, Limitation on Investments			$ 75,000
Debt Covenant, Limitation on Capital Expenditures			125,000
Debt Covenant, Required Sale Proceed Pay-Down			100,000
Debt Covenant, Liquidity Requirement			$ 250,000
Unsecured Revolving Variable Rate Credit Facility, Variable Rate, Due February 27, 2022 [Member] | covenant relief period [Member] | Unsecured Debt [Member]
Subsequent Event [Line Items]
Long-term Debt, Spread Increase, Percentage			0.25%
Subsequent Event [Member] | Unsecured Revolving Variable Rate Credit Facility, Variable Rate, Due February 27, 2022 [Member] | covenant relief period [Member] | Unsecured Debt [Member]
Subsequent Event [Line Items]
Debt Covenant, Limitation on Investments	$ 50,000	$ 175,000
Debt Covenant, Limitation on Capital Expenditures	$ 50,000	175,000
Debt Covenant, Required Sale Proceed Pay-Down		150,000
Debt Covenant, Liquidity Requirement		$ 500,000
Long-term Debt, Spread Increase, Percentage		0.35%