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Real Estate and Intangible Assets - Summary of Acquired Properties (Details) $ in Thousands |  |  |  |  |  | 9 Months Ended |
--- | --- | --- | --- | --- | --- | --- | ---
Jul. 31, 2017 USD ($) ft² | Jul. 07, 2017 USD ($) ft² | Jun. 22, 2017 USD ($) ft² | Sep. 12, 2016 USD ($) ft² | May 26, 2016 USD ($) ft² | Sep. 30, 2017 USD ($) ft² property | Sep. 30, 2016 USD ($) ft² property | Jul. 25, 2014 ft²
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Square Footage (unaudited) | ft² |  |  |  |  |  |  |  | 81,371
Purchase Price |  |  |  |  |  | $ 94,421 | $ 40,900 |
Number of properties acquired | property |  |  |  |  |  | 5 | 2 |
Series of Property Acquisitions |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Square Footage (unaudited) | ft² |  |  |  |  |  | 666,451 | 226,286 |
Lease Term |  |  |  |  |  | 10 years 8 months 12 days | 7 years 9 months 18 days |
Purchase Price |  |  |  |  |  | $ 94,421 | $ 40,900 |
Acquisition Expenses |  |  |  |  |  | 1,171 | 179 |
Annualized GAAP Rent |  |  |  |  |  | 10,776 | 3,367 |
Debt Issued or Assumed |  |  |  |  |  | 54,887 | 24,000 |
Conshohocken, Pennsylvania |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Square Footage (unaudited) | ft² |  |  | 60,016 |  |  |  |  |
Lease Term |  |  | 8 years 6 months |  |  |  |  |
Purchase Price |  |  | $ 15,700 |  |  |  |  |
Annualized GAAP Rent |  |  | 1,700 |  |  |  |  |
Debt assumed |  |  | $ 11,200 |  |  |  |  |
Stated interest rate (as percent) |  |  | 1.80% |  |  |  |  |
Conshohocken, Pennsylvania | Interest rate swap |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Debt assumed |  |  | $ 11,200 |  |  |  |  |
Interest rate swap |  |  | $ 40 |  |  | $ 200 |  |
Conshohocken, Pennsylvania | Interest rate swap | LIBOR |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Basis spread |  |  | 3.55% |  |  |  |  |
Philadelphia, Pennsylvania |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Square Footage (unaudited) | ft² |  | 300,000 |  |  |  |  |  |
Lease Term |  | 15 years 4 months 24 days |  |  |  |  |  |
Purchase Price |  | $ 27,100 |  |  |  |  |  |
Annualized GAAP Rent |  | 2,300 |  |  |  |  |  |
Debt Issued or Assumed |  | $ 14,900 |  |  |  |  |  |
Stated interest rate (as percent) |  | 3.75% |  |  |  |  |  |
Maitland, Florida |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Square Footage (unaudited) | ft² | 306,435 |  |  |  |  |  |  |
Lease Term | 8 years 7 months 6 days |  |  |  |  |  |  |
Purchase Price | $ 51,600 |  |  |  |  |  |  |
Annualized GAAP Rent | 6,800 |  |  |  |  |  |  |
Debt Issued or Assumed | $ 28,800 |  |  |  |  |  |  |
Stated interest rate (as percent) | 3.89% |  |  |  |  |  |  |
Number of properties acquired | property |  |  |  |  |  | 3 |  |
Salt Lake City, Utah |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Square Footage (unaudited) | ft² |  |  |  |  | 107,062 |  |  |
Lease Term |  |  |  |  | 6 years |  |  |
Purchase Price |  |  |  |  | $ 17,000 |  |  |
Annualized GAAP Rent |  |  |  |  | 1,400 |  |  |
Debt Issued or Assumed |  |  |  |  | $ 9,900 |  |  |
Fort Lauderdale, FL |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Square Footage (unaudited) | ft² |  |  |  | 119,224 |  |  |  |
Lease Term |  |  |  | 9 years |  |  |  |
Purchase Price |  |  |  | $ 23,900 |  |  |  |
Annualized GAAP Rent |  |  |  | 2,000 |  |  |  |
Debt Issued or Assumed |  |  |  | $ 14,100 |  |  |  |
Asset acquisition |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |
Purchase Price |  |  |  |  |  | $ 94,421 | $ 0 |

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