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INVESTMENT ACTIVITY (Details) $ / shares in Units, £ in Millions |  |  |  |  |  |  |  |  |  |  |  |  | 1 Months Ended | 2 Months Ended | 3 Months Ended | 12 Months Ended
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Jun. 02, 2017 USD ($) | Apr. 12, 2017 USD ($) shares | Aug. 12, 2016 USD ($) | Apr. 18, 2016 USD ($) shares | Apr. 06, 2016 USD ($) | Dec. 15, 2015 USD ($) facility | Oct. 08, 2015 USD ($) item | Oct. 02, 2015 GBP (£) | Oct. 02, 2015 USD ($) | May 14, 2015 USD ($) shares | Mar. 18, 2015 USD ($) facility | Nov. 03, 2014 USD ($) facility | Aug. 25, 2014 USD ($) facility | Jan. 31, 2016 item | Dec. 31, 2015 item | Jun. 30, 2014 USD ($) facility | Jan. 31, 2016 item | Dec. 31, 2015 | Dec. 31, 2017 USD ($) property item facility $ / shares shares | Dec. 31, 2016 USD ($) property item facility | Dec. 31, 2015 USD ($) facility | Dec. 31, 2008
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales of facilities, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 9,041,000 |
Storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 4,161,715,000 | $ 3,998,180,000 |  |
Restricted cash |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3,890,000 | $ 7,893,000 |  |
Gain from sale of real estate, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 17,567,000 |
OP units issued (in shares) | shares |  |  |  | 61,224 |  |  |  |  |  | 20,408 |  |  |  |  |  |  |  |  |  |  |  |
Issuance of OP Shares |  |  |  | $ 1,500,000 |  |  |  |  |  | $ 500,000 |  |  |  |  |  |  |  |  |  |  |  |
Acquisition of noncontrolling interest |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,033,000 |  |  |
USIFB, LLP |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate sale price |  |  |  |  |  |  |  | £ 6.5 | $ 9,900,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from sales of facilities, net |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 7,000,000 |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  | 97.00% | 97.00% |  |  |  |  |  |  |  |  |  |  |  | 97.00% | 97.00%
Number of assets sold | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |
Gain from sale of real estate, net |  |  |  |  |  |  |  |  | $ 3,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Foreign currency translation loss |  |  |  |  |  |  |  |  | $ 1,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Self storage in operation |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 281,300,000 |  |  |
Self storage under construction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Development costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 121,000,000 |  |  |
Expected construction cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 232,600,000 |  |  |
Number of facilities under contract | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 |  |  |
Self-storage facilities located in New York |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.00% |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 81,200,000 |  |  |
Self-storage Facility in Arlington, VA |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.00% |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 17,100,000 |  |  |
Self-storage Facility in Washington DC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 27,800,000 |  |  |
Self-storage Facility In North Palm Beach, FL |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 9,700,000 |  |  |
Self-storage Facility in Queens, NY |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 31,800,000 |  |  |
Self Storage Facility in Queens, NY I |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash paid for acquisition |  |  |  |  | $ 12,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.00% |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 17,400,000 |  |  |
Acquisition of remaining interest in real estate ventures (as a percent) |  |  |  |  | 49.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash paid for acquisition of remaining interest in real estate ventures |  |  |  |  | $ 12,500,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage Facility in Brooklyn, NY |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 51.00% |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 49,300,000 |  |  |
Self Storage Facility in Brooklyn, NY I |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash paid for acquisition | $ 9,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.00% | 100.00% |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 14,800,000 |  |  |
Minority ownership interest (as a percent) | 0.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition of remaining interest in real estate ventures (as a percent) | 10.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash paid for acquisition of remaining interest in real estate ventures | $ 9,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition of noncontrolling interest | 8,600,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of debt | $ 9,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage Facility in Bronx, NY |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash paid for acquisition |  |  | $ 17,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 100.00% |  |  |
Number of facilities, construction completed and opened |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1 |  |  |
Total Construction Costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 32,200,000 |  |  |
Acquisition of remaining interest in real estate ventures (as a percent) |  |  | 49.00% |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash paid for acquisition of remaining interest in real estate ventures |  |  | $ 17,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self Storage Facilities in Bronx, NY and Brooklyn, NY |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest held by the entity (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 51.00% |  |
Number of joint ventures | item |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |
2017 Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities acquired | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7 |  |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 80,650,000 |  |  |
Summary of the amounts of revenue and earnings of the 2016 and 2015 acquisitions since the acquisition dates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total revenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,572,000 |  |  |
Net loss |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (1,330,000) |  |  |
2017 Acquisitions | Self storage under construction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 33,000,000 |  |  |
Contract amount to purchase real estate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,000,000 |  |  |
Number of facilities under contract | item |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |
2017 Acquisitions | Self-storage facilities located in US |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities acquired | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6 |  |  |
Number of self-storage facilities acquired upon completion of construction | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 |  |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 69,500,000 |  |  |
Intangible value of the in-place leases |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,200,000 |  |  |
Estimated life |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 months |  |  |
Amortization expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 1,500,000 |  |  |
Number of properties, assumed mortgage | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |
Units issued |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 12,300,000 |  |  |
Assumed mortgage debt, at fair value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6,200,000 |  |  |
Outstanding principal balance of mortgage debt assumed on acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,900,000 |  |  |
Premium on debt assumed on acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 300,000 |  |  |
2016 Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities acquired |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 28 | 28 |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 403,550,000 |  |
Intangible value of the in-place leases |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 18,800,000 |  |  |
Estimated life |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 months |  |  |
Amortization expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 8,300,000 | 10,500,000 |  |
Number of properties, assumed mortgage | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |
Assumed mortgage debt, at fair value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6,500,000 |  |  |
Outstanding principal balance of mortgage debt assumed on acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6,300,000 |  |  |
Premium on debt assumed on acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 |  |  |
Number of facilities not yet closed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 |  |  |
2015 Acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities acquired | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 29 |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 292,362,000 |
2015 Acquisitions | PSI |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  |  |  | $ 109,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible value of the in-place leases |  |  |  |  |  | $ 6,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated life |  |  |  |  |  | 12 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amortization expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 6,100,000 | 600,000 |  |
2015 Acquisitions | HSRE |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities | facility |  |  |  |  |  |  |  |  |  |  |  |  | 26 |  |  |  |  |  |  |  |  |
Number of self-storage facilities acquired | facility |  |  |  |  |  |  |  |  |  |  |  | 22 |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  | $ 27,500,000 | $ 195,500,000 | $ 223,000,000 |  |  |  |  |  |  | $ 2,700,000 |  |
Estimated life |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 months |  |
Amortization expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 700,000 | $ 2,000,000 |  |
Number of properties, assumed mortgage | facility |  |  |  |  |  |  |  |  |  |  | 4 |  |  |  |  |  |  |  |  |  |  |
2015 Acquisitions | Self storage under construction | PSI |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities | facility |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  |  |  | $ 6,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 Acquisitions | Self-storage facilities located in US |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 13 |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 155,000,000 |  |
Intangible value of the in-place leases |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 10,700,000 |  |
Estimated life |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 months |  |
Amortization expense |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 6,000,000 | $ 4,700,000 |  |
Number of properties, assumed mortgage | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |
Assumed mortgage debt, at fair value |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 2,700,000 |  |
Outstanding principal balance of mortgage debt assumed on acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,500,000 |  |
Premium on debt assumed on acquisitions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 200,000 |  |
Number of facilities not yet closed |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |
Real Estate Acquisition Expected in 2018 | Self storage under construction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities acquired upon completion of construction | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |
2015 Dispositions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities acquired | item |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 | 1 |  | 3 |  |  |  |  |
Aggregate sale price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 36,400,000 |  |
2015 Dispositions | Properties in Texas and Florida |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate sale price |  |  |  |  |  |  | $ 37,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Gain from sale of real estate, net |  |  |  |  |  |  | $ 14,400,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities acquired | property |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 7 | 28 |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 80,700,000 | $ 403,600,000 |  |
Self-storage facilities | 2015 Acquisitions | PSI |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of self-storage facilities | facility |  |  |  |  |  | 12 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  |  |  | $ 115,800,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Texas | 2015 Dispositions | Properties in Texas and Florida |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of assets sold | item |  |  |  |  |  |  | 7 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Florida | 2015 Dispositions | Properties in Texas and Florida |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of assets sold | item |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
New York | Self storage under construction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of facilities under contract | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 |  |  |
Massachusetts | Self storage under construction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of facilities under contract | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |
New Jersey | Self storage under construction |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of facilities under contract | facility |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 |  |  |
Illinois |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash paid for acquisition |  | $ 9,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 9,700,000 |  |  |
Contract amount to purchase real estate |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11,200,000 |  |  |
Units issued (in shares) | shares |  | 58,400 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total consideration |  | $ 11,200,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Cash paid for acquisition of remaining interest in real estate ventures |  | $ 9,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 9,700,000 |  |  |
Class C units | Illinois |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Self-storage facilities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Units issued (in shares) | shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 58,400 |  |  |
Stated value (in dollars per share) | $ / shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 25 |  |  |
Distribution rate (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3.00% |  |  |

X
- References No definition available. + Details
Name: | cube_BusinessAcquisitionProFormaInformationOfAcquireeSinceAcquisitionDateActualAbstract
Namespace Prefix: | cube_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of total construction cost expected of the projects. + References No definition available. + Details
Name: | cube_ConstructionCostExpected
Namespace Prefix: | cube_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Represents the contract amount to purchase real estate as of the balance sheet date. + References No definition available. + Details
Name: | cube_ContractToAcquireRealEstateAmount
Namespace Prefix: | cube_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The number of self-storage facilities with construction completed and opened for operation during the period. + References No definition available. + Details
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Namespace Prefix: | cube_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the number of facilities not yet closed. + References No definition available. + Details
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Namespace Prefix: | cube_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the number of facilities under contract. + References No definition available. + Details
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Namespace Prefix: | cube_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the information pertaining to number of joint ventures. + References No definition available. + Details
Name: | cube_NumberOfJointVentures
Namespace Prefix: | cube_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of real estate properties that were acquired. + References No definition available. + Details
Name: | cube_NumberOfRealEstatePropertiesAcquired
Namespace Prefix: | cube_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of real estate acquired properties of which mortgages were assumed. + References No definition available. + Details
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Namespace Prefix: | cube_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of real estate properties acquired upon completion of construction and issuance of certificate of occupancy. + References No definition available. + Details
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Namespace Prefix: | cube_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of real estate properties that were sold. + References No definition available. + Details
Name: | cube_NumberOfRealEstatePropertiesSold
Namespace Prefix: | cube_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of self-storage facilities involved in transaction. + References No definition available. + Details
Name: | cube_NumberOfSelfStorageFacilities
Namespace Prefix: | cube_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the intangible lease assets recorded as part of the real estate acquisition. + References No definition available. + Details
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Namespace Prefix: | cube_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Represents the debt assumed on real estate acquisition. + References No definition available. + Details
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Namespace Prefix: | cube_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Represents the premium on debt assumed on real estate acquisition. + References No definition available. + Details
Name: | cube_RealEstatePropertiesPremiumOnDebtAssumed
Namespace Prefix: | cube_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Represents the number of operating partnership units issued during the period. + References No definition available. + Details
Name: | cube_StockIssuedDuringPeriodNumberOfOperatingUnits
Namespace Prefix: | cube_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the value of the operating units issued during the period. + References No definition available. + Details
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Namespace Prefix: | cube_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Annual distribution rate of stock classified as temporary equity. + References No definition available. + Details
Name: | cube_TemporaryEquityAnnualDistributionRate
Namespace Prefix: | cube_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Shares classified as temporary equity issued during the period. + References No definition available. + Details
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Namespace Prefix: | cube_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition The aggregate expense charged against earnings to allocate the cost of intangible assets (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16225-109274 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 30 -Section 50 -Paragraph 2 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of voting equity interests acquired at the acquisition date in the business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463 + Details
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Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6578-128477 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6911251&loc=d3e6613-128477 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition This element represents the amount of earnings or loss of the acquiree since the acquisition date included in the consolidated income statement for the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition This element represents the amount of revenue of the acquiree since the acquisition date included in the consolidated income statement for the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=65885119&loc=d3e1392-128463 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=73530397&loc=d3e4845-128472 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The aggregate costs related to construction and development services during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2) -URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The current amount of expenditures for a real estate project that has not yet been completed. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.10) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Phase -URI http://asc.fasb.org/extlink&oid=49177889 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount before tax of foreign currency transaction realized and unrealized gain (loss) recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450222&loc=d3e30840-110895 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64836518&loc=d3e30700-110894 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=64836518&loc=d3e30690-110894 + Details
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X
- Definition The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585 + Details
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- Definition Decrease in noncontrolling interest (for example, but not limited to, redeeming or purchasing the interests of noncontrolling shareholders, issuance of shares (interests) by the non-wholly owned subsidiary to the parent entity for other than cash, and a buyback of shares (interest) by the non-wholly owned subsidiary from the noncontrolling interests). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 23 -URI http://asc.fasb.org/extlink&oid=68079674&loc=SL4569655-111683 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=68079674&loc=SL4616395-111683 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity. + References No definition available. + Details
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Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3213-108585 + Details
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