FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Interest rate swaps
FAIR VALUE OF FINANCIAL INSTRUMENTS
Fair value of derivative assets	$ 474	$ 0
Level 2 \| Fair value
FAIR VALUE OF FINANCIAL INSTRUMENTS
Debt, consisting of mortgage notes, unsecured term loan, unsecured senior notes and unsecured line of credit	2,555,030	2,968,865
Level 2 \| Carrying amount
FAIR VALUE OF FINANCIAL INSTRUMENTS
Debt, consisting of mortgage notes, unsecured term loan, unsecured senior notes and unsecured line of credit	2,435,590	2,777,527
Level 2 \| Interest rate swaps
FAIR VALUE OF FINANCIAL INSTRUMENTS
Fair value of derivative assets	$ 474

Fair value of asset associated with financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=28370219&loc=SL20226003-175313

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 20

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=20225523&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (a),(c)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624163-113959

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant