Date the declared dividend will be paid, in CCYY-MM-DD format.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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The per share amount of a dividend declared, but not paid, as of the financial reporting date.

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Date the dividend to be paid was declared, in CCYY-MM-DD format.

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Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

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Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

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Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

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SUBSEQUENT EVENTS (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	Jul. 31, 2018	Feb. 28, 2018	Mar. 07, 2017	Jul. 20, 2018	Jun. 30, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Commitment amount					$ 673,090	$ 523,821
Series A Preferred Stock [Member]
Subsequent Event [Line Items]
Dividends declared date		Feb. 28, 2018	May 02, 2018
Dividend payable, amount per share		$ 12.12	$ 16.07
Dividends payable date		Apr. 13, 2018	Jul. 13, 2018
Dividends payable, date of record		Apr. 01, 2018	Jul. 01, 2018
Series A Preferred Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends declared date	Jul. 31, 2018
Dividends payable date	Oct. 15, 2018
Dividends payable, date of record	Oct. 01, 2018
Series B Preferred Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends declared date	Jul. 31, 2018
Dividend payable, amount per share	$ 0.4375
Dividends payable date	Oct. 15, 2018
Dividends payable, date of record	Oct. 01, 2018
Common Stock [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Dividends declared date	Jul. 31, 2018
Dividend payable, amount per share	$ 0.35
Dividends payable date	Oct. 15, 2018
Dividends payable, date of record	Oct. 01, 2018
Development Property Investments [Member]
Subsequent Event [Line Items]
Commitment amount					$ 583,784	$ 517,839
Boston, Massachusetts MSA [Member] \| Subsequent Event [Member]
Subsequent Event [Line Items]
Commitment amount				$ 3,800