Indebtedness - Summary of Indebtedness (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Mortgage Loans Payable, Net		$ 301,661	$ 450,056
Senior Unsecured Notes, Net		544,204	246,673
Unsecured Term Loans, Net		456,016	455,768
Unsecured Credit Facility		100,000	144,500
2027 Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, 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]
Senior Unsecured Notes, 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]
Senior Unsecured Notes, 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]
Senior Unsecured Notes, 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]
Senior Unsecured Notes, Gross		$ 150,000	0
Interest Rate		3.86%
Effective Interest Rate		3.86%
Maturity Date		Feb. 15, 2028
2029 Private Placement Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, Gross		$ 75,000	75,000
Interest Rate		4.40%
Effective Interest Rate		4.40%
Maturity Date		Apr. 20, 2029
2030 Private Placement Notes
Debt Instrument [Line Items]
Senior Unsecured Notes, Gross		$ 150,000	0
Interest Rate		3.96%
Effective Interest Rate		3.96%
Maturity Date		Feb. 15, 2030
2014 Unsecured Term Loan (A)
Debt Instrument [Line Items]
Unsecured Term Loans, Gross	[1]	$ 200,000	200,000
Interest Rate	[1]	3.39%
Maturity Date	[1]	Jan. 29, 2021
2015 Unsecured Term Loan (A)
Debt Instrument [Line Items]
Unsecured Term Loans, Gross	[1]	$ 260,000	260,000
Interest Rate	[1]	2.89%
Maturity Date	[1]	Sep. 12, 2022
Mortgage Loans Payable
Debt Instrument [Line Items]
Mortgage Loans Payable, Gross		$ 303,093	451,602
Unamortized Debt Issuance Costs		(1,644)	(1,806)
Unamortized Premiums		212	260
Mortgage Loans Payable, Net		$ 301,661	450,056
Maturity Date Range, Start		Jul. 01, 2019
Maturity Date Range, End		Aug. 01, 2028
Senior Unsecured Notes
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		$ (4,285)	(1,814)
Senior Unsecured Notes, Gross		548,571	248,571
Unamortized Discounts		82	84
Senior Unsecured Notes, Net		544,204	246,673
Unsecured Term Loan
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		(3,984)	(4,232)
Unsecured Term Loans, Gross		460,000	460,000
Unsecured Term Loans, Net		456,016	455,768
Unsecured Credit Facility
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		(4,495)	(4,781)
Unsecured Credit Facility	[2]	$ 100,000	$ 144,500
Interest Rate	[2]	2.83%
Maturity Date	[2]	Oct. 29, 2021
Minimum | Mortgage Loans Payable
Debt Instrument [Line Items]
Interest Rate		4.03%
Effective Interest Rate		3.82%
Maximum | Mortgage Loans Payable
Debt Instrument [Line Items]
Interest Rate		8.26%
Effective Interest Rate		8.26%

[1] The interest rate at March 31, 2018 also reflects the interest rate protection agreements 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 $4,495 and $4,781 as of March 31, 2018 and December 31, 2017, respectively, which are included in prepaid expenses and other assets on the consolidated balance sheets.