Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
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-Subparagraph (SX 210.5-02.22)
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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The amount of debt discount (net of debt premium) that was originally recognized at the issuance of the instrument that has yet to be amortized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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- Definition

Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Indebtedness - Schedule of Outstanding Indebtedness (Details) - USD ($)	Dec. 31, 2016	Dec. 15, 2016	Feb. 16, 2016	Dec. 31, 2015	Jan. 29, 2015
Debt Instrument [Line Items]
Outstanding indebtedness	$ 1,151,634,000			$ 1,711,666,000
Unamortized net premiums, discounts and deferred financing fees	(9,967,000)			(14,550,000)
Total	$ 1,141,667,000			1,697,116,000
Unsecured revolving credit facility, at LIBOR plus a premium
Debt Instrument [Line Items]
Interest rate stated percentage	2.02%
Outstanding indebtedness	$ 0			0
5-year unsecured term loan, at LIBOR plus a premium
Debt Instrument [Line Items]
Interest rate stated percentage	2.17%
Outstanding indebtedness	$ 200,000,000			200,000,000
Total	$ 200,000,000				$ 200,000,000.0
7-year unsecured term loan, at LIBOR plus a premium
Debt Instrument [Line Items]
Interest rate stated percentage	2.57%
Outstanding indebtedness	$ 200,000,000			200,000,000
Total	$ 200,000,000.0				$ 200,000,000.0
Unsecured floating rate debt
Debt Instrument [Line Items]
Interest rate stated percentage	2.37%
Outstanding indebtedness	$ 400,000,000			400,000,000
6.25% Senior Unsecured Notes due 2016
Debt Instrument [Line Items]
Interest rate stated percentage	0.00%		6.25%
Outstanding indebtedness	$ 0			139,104,000
6.25% Senior Unsecured Notes due 2017
Debt Instrument [Line Items]
Interest rate stated percentage	0.00%	6.25%
Outstanding indebtedness	$ 0			250,000,000
6.65% Senior Unsecured Notes due 2018
Debt Instrument [Line Items]
Interest rate stated percentage	6.65%
Outstanding indebtedness	$ 250,000,000			250,000,000
5.875% Senior Unsecured Notes due 2020
Debt Instrument [Line Items]
Interest rate stated percentage	5.88%
Outstanding indebtedness	$ 250,000,000			250,000,000
5.75% Senior Unsecured Notes due 2042
Debt Instrument [Line Items]
Interest rate stated percentage	5.75%
Outstanding indebtedness	$ 175,000,000			175,000,000
Unsecured fixed rate debt
Debt Instrument [Line Items]
Interest rate stated percentage	6.13%
Outstanding indebtedness	$ 675,000,000			1,064,104,000
Mortgage Notes Payable Encumbering Parkshore Plaza
Debt Instrument [Line Items]
Interest rate stated percentage	5.67%
Outstanding indebtedness	$ 41,275,000			41,275,000
Mortgage Notes Payable Encumbering 1735 Market Street
Debt Instrument [Line Items]
Interest rate stated percentage	0.00%
Outstanding indebtedness	$ 0			169,612,000
Mortgage Notes Payable Encumbering 206 East 9th Street
Debt Instrument [Line Items]
Interest rate stated percentage	5.69%
Outstanding indebtedness	$ 27,041,000			27,515,000
Mortgage Notes Payable Encumbering 33 Stiles Lane
Debt Instrument [Line Items]
Interest rate stated percentage	6.75%
Outstanding indebtedness	$ 2,415,000			2,785,000
Mortgage Notes Payable Encumbering 97 Newberry Road
Debt Instrument [Line Items]
Interest rate stated percentage	5.71%
Outstanding indebtedness	$ 5,903,000			6,375,000
Secured Fixed Rate Debt
Debt Instrument [Line Items]
Interest rate stated percentage	5.71%
Outstanding indebtedness	$ 76,634,000			$ 247,562,000