STORAGE FACILITIES - Activity (Details) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016 USD ($) facility	Dec. 31, 2015 USD ($) facility
2016 Acquisitions
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	17
Purchase Price | $	$ 270,925
2016 Acquisitions | Metro DC Asset One
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 21,000
2016 Acquisitions | Texas Asset Nineteen
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	2
Purchase Price | $	$ 24,800
2016 Acquisitions | New York Asset Four
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 48,500
2016 Acquisitions | Texas Asset Twenty
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 11,600
2016 Acquisitions | Connecticut Asset
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 19,000
2016 Acquisitions | Texas Asset Twenty-one
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 11,600
2016 Acquisitions | Florida Assets Thirteen
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	3
Purchase Price | $	$ 47,925
2016 Acquisitions | Colorado Asset Two
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 11,350
2016 Acquisitions | Texas Asset Twenty-Two
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 11,600
2016 Acquisitions | Texas Asset Twenty-Three
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 10,100
2016 Acquisitions | Texas Asset Twenty-Four
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 10,800
2016 Acquisitions | Illinois Asset Two
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 12,350
2016 Acquisitions | Illinois Asset Three
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 16,000
2016 Acquisitions | Massachusetts Asset Three
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility	1
Purchase Price | $	$ 14,300
2015 Acquisitions
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		29
Purchase Price | $		$ 292,362
2015 Acquisitions | Texas Asset Seventeen
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 7,295
2015 Acquisitions | HSRE Assets Two
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		4
Purchase Price | $		$ 27,500
2015 Acquisitions | Arizona Asset Five
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 7,900
2015 Acquisitions | Tennessee Assets
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 6,575
2015 Acquisitions | Texas Asset Eighteen
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 15,795
2015 Acquisitions | Florida Assets Eleven
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 7,300
2015 Acquisitions | Arizona Asset Six
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 10,100
2015 Acquisitions | Florida Assets Twelve
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 10,500
2015 Acquisitions | Texas Asset Eight
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 14,200
2015 Acquisitions | Maryland Asset Three
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 17,000
2015 Acquisitions | Maryland Asset Four
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 19,200
2015 Acquisitions | New York/New Jersey Assets
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		2
Purchase Price | $		$ 24,823
2015 Acquisitions | New Jersey Assets
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		1
Purchase Price | $		$ 14,350
2015 Acquisitions | PSI Assets
STORAGE FACILITIES
Number of Facilities, acquisitions (in properties) | facility		12
Purchase Price | $		$ 109,824
Dispositions
STORAGE FACILITIES
Number of Facilities, dispositions (in properties) | facility		8
Sale Price | $		$ 37,800
Dispositions | Texas Asset One
STORAGE FACILITIES
Number of Facilities, dispositions (in properties) | facility		7
Sale Price | $		$ 28,000
Dispositions | Florida Assets
STORAGE FACILITIES
Number of Facilities, dispositions (in properties) | facility		1
Sale Price | $		$ 9,800