Indebtedness - Summary of Indebtedness (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 1,651,674
Unsecured Credit Facility		320,000	$ 158,000
2027 Notes
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 6,070	6,070
Interest Rate		7.15%
Effective Interest Rate		7.11%
Maturity Date		May 15, 2027
2028 Notes
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 31,901	31,901
Interest Rate		7.60%
Effective Interest Rate		8.13%
Maturity Date		Jul. 15, 2028
2032 Notes
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 10,600	10,600
Interest Rate		7.75%
Effective Interest Rate		7.87%
Maturity Date		Apr. 15, 2032
2027 Private Placement Notes
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 125,000	125,000
Interest Rate		4.30%
Effective Interest Rate		4.30%
Maturity Date		Apr. 20, 2027
2028 Private Placement Notes
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 150,000	150,000
Interest Rate		3.86%
Effective Interest Rate		3.86%
Maturity Date		Feb. 15, 2028
2029 Private Placement Notes
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 75,000	75,000
Interest Rate		4.40%
Effective Interest Rate		4.40%
Maturity Date		Apr. 20, 2029
2029 II Private Placement Notes
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 150,000	150,000
Interest Rate		3.97%
Effective Interest Rate		4.23%
Maturity Date		Jul. 23, 2029
2030 Private Placement Notes
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 150,000	150,000
Interest Rate		3.96%
Effective Interest Rate		3.96%
Maturity Date		Feb. 15, 2030
2014 Unsecured Term Loan (A)
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 200,000	200,000
Interest Rate	[1]	3.39%
Maturity Date	[1]	Jan. 29, 2021
2015 Unsecured Term Loan (A)
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 260,000	260,000
Interest Rate	[1]	2.89%
Maturity Date	[1]	Sep. 12, 2022
Mortgage Loans Payable
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 173,103	174,360
Unamortized Debt Issuance Costs		(593)	(675)
Long-term Debt		$ 172,510	173,685
Maturity Date Range, Start		Jul. 01, 2020
Maturity Date Range, End		Aug. 01, 2028
Senior Unsecured Notes
Debt Instrument [Line Items]
Long-term Debt, Gross		$ 698,571	698,571
Unamortized Debt Issuance Costs		(4,357)	(4,485)
Unamortized Discounts		70	71
Long-term Debt		694,144	694,015
Unsecured Term Loan
Debt Instrument [Line Items]
Long-term Debt, Gross		460,000	460,000
Unamortized Debt Issuance Costs		(1,871)	(2,135)
Long-term Debt		458,129	457,865
Unsecured Credit Facility
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		(1,986)	(2,300)
Unsecured Credit Facility	[2]	$ 320,000	$ 158,000
Interest Rate	[1]	2.09%
Maturity Date	[2]	Oct. 29, 2021
Minimum | Mortgage Loans Payable
Debt Instrument [Line Items]
Interest Rate		4.03%
Effective Interest Rate		4.03%
Maximum | Mortgage Loans Payable
Debt Instrument [Line Items]
Interest Rate		6.50%
Effective Interest Rate		6.50%

[1] The interest rate at March 31, 2020 also reflects the derivative instruments we entered into to effectively convert the variable rate to a fixed rate. See Note 10.

[2] The maturity date may be extended an additional year at our election, subject to certain restrictions. Amounts exclude unamortized debt issuance costs of $1,986 and $2,300 as of March 31, 2020 and December 31, 2019, respectively, which are included in the line item Prepaid Expenses and Other Assets, Net.