Debt Obligations - Consolidated Debt Obligations Outstanding (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2020	Dec. 31, 2019
Consolidated debt obligations
Plus: premiums/(discounts), net	$ 10,312
Less: deferred financing costs	(9,814)
Outstanding indebtedness	2,192,600	$ 2,144,418
Secured Debt
Consolidated debt obligations
Long-term debt, gross	313,492	315,437
Plus: premiums/(discounts), net	(1,289)	(1,383)
Less: deferred financing costs	(202)	(242)
Total mortgage indebtedness	312,001	313,812
Unsecured Debt
Consolidated debt obligations
Long-term debt, gross	1,878,610	1,828,610
Plus: premiums/(discounts), net	11,601	12,090
Less: deferred financing costs	(9,612)	(10,094)
Total unsecured indebtedness	1,880,599	1,830,606
Unsecured Debt \| $600 million Unsecured Credit Facility
Consolidated debt obligations
Long-term debt, gross	50,000	0
Unsecured Debt \| Seven-Year Term Loan - Swapped to fixed
Consolidated debt obligations
Long-term debt, gross	$ 250,000	250,000
Effective interest rate	2.87%
Unsecured Debt \| $350.0M 3.95% Guaranteed Notes due 2023
Consolidated debt obligations
Long-term debt, gross	$ 350,000	350,000
Effective interest rate	3.87%
Unsecured Debt \| $350.0M 4.10% Guaranteed Notes due 2024
Consolidated debt obligations
Long-term debt, gross	$ 350,000	350,000
Effective interest rate	3.78%
Unsecured Debt \| $450.0M 3.95% Guaranteed Notes due 2027
Consolidated debt obligations
Long-term debt, gross	$ 450,000	450,000
Effective interest rate	4.03%
Unsecured Debt \| $350.0M 4.55% Guaranteed Notes due 2029
Consolidated debt obligations
Long-term debt, gross	$ 350,000	350,000
Effective interest rate	4.30%
Unsecured Debt \| Indenture IA (Preferred Trust I)
Consolidated debt obligations
Long-term debt, gross	$ 27,062	27,062
Unsecured Debt \| Indenture IB (Preferred Trust I) - Swapped to fixed
Consolidated debt obligations
Long-term debt, gross	$ 25,774	25,774
Effective interest rate	3.30%
Unsecured Debt \| Indenture II (Preferred Trust II)
Consolidated debt obligations
Long-term debt, gross	$ 25,774	25,774
LIBOR \| Unsecured Debt \| $600 million Unsecured Credit Facility
Consolidated debt obligations
Spread on variable rate	1.10%
LIBOR \| Unsecured Debt \| Indenture IA (Preferred Trust I)
Consolidated debt obligations
Spread on variable rate	1.25%
LIBOR \| Unsecured Debt \| Indenture II (Preferred Trust II)
Consolidated debt obligations
Spread on variable rate	1.25%
Two Commerce Square \| Secured Debt
Consolidated debt obligations
Long-term debt, gross	$ 107,948	108,472
Effective interest rate	4.51%
One Commerce Square \| Secured Debt
Consolidated debt obligations
Long-term debt, gross	$ 115,647	116,571
Effective interest rate	3.64%
Four Tower Bridge \| Secured Debt
Consolidated debt obligations
Long-term debt, gross	$ 9,230	9,291
Effective interest rate	4.50%
Two Logan Square \| Secured Debt
Consolidated debt obligations
Long-term debt, gross	$ 80,667	$ 81,103
Effective interest rate	3.98%

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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