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Real Estate and Intangible Assets - Summary of Properties Acquired (Detail) $ in Thousands |  |  |  |  |  |  |  | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Dec. 01, 2017 USD ($) ft² | Jul. 31, 2017 USD ($) ft² property | Jul. 07, 2017 USD ($) ft² | Jun. 22, 2017 USD ($) ft² | Dec. 14, 2016 USD ($) ft² | Sep. 12, 2016 USD ($) ft² | May 26, 2016 USD ($) ft² | Dec. 31, 2017 USD ($) ft² | Dec. 31, 2016 USD ($) ft² | Jul. 25, 2014 ft²
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate Square Footage | ft² |  |  |  |  |  |  |  |  |  | 81,371
Aggregate Purchase Price |  |  |  |  |  |  |  | $ 132,157 | $ 66,570 |
Acquisition Expenses |  |  |  |  |  |  |  | 1,400 |  |
Number of properties in portfolio | property |  | 3 |  |  |  |  |  |  |  |
Derivative asset |  |  |  |  |  |  |  | 504 | 101 |
Accumulated other comprehensive income |  |  |  |  |  |  |  | $ (35) | $ 0 |
Series of Property Acquisitions [Member] |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate Square Footage | ft² |  |  |  |  |  |  |  | 871,038 | 329,620 |
Lease Term |  |  |  |  |  |  |  | 10 years 1 month 6 days | 10 years 6 months |
Aggregate Purchase Price |  |  |  |  |  |  |  | $ 132,157 | $ 66,570 |
Acquisition Expenses |  |  |  |  |  |  |  | 1,356 | 179 |
Aggregate Annualized GAAP Rent |  |  |  |  |  |  |  | 15,507 | 5,589 |
Aggregate Debt Issued or Assumed |  |  |  |  |  |  |  | $ 54,887 | $ 38,800 |
Conshohocken, PA |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate Square Footage | ft² |  |  |  | 60,016 |  |  |  |  |  |
Lease Term |  |  |  | 8 years 6 months |  |  |  |  |  |
Aggregate Purchase Price |  |  |  | $ 15,700 |  |  |  |  |  |
Aggregate Annualized GAAP Rent |  |  |  | 1,700 |  |  |  |  |  |
Noncash or part noncash acquisition, debt assumed |  |  |  | $ 11,200 |  |  |  |  |  |
Philadelphia, PA |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate Square Footage | ft² |  |  | 300,000 |  |  |  |  |  |  |
Lease Term |  |  | 15 years 4 months 24 days |  |  |  |  |  |  |
Aggregate Purchase Price |  |  | $ 27,100 |  |  |  |  |  |  |
Aggregate Annualized GAAP Rent |  |  | 2,300 |  |  |  |  |  |  |
Aggregate Debt Issued or Assumed |  |  | $ 14,900 |  |  |  |  |  |  |
Maitland, Florida |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate Square Footage | ft² |  | 306,435 |  |  |  |  |  |  |  |
Lease Term |  | 8 years 7 months 6 days |  |  |  |  |  |  |  |
Aggregate Purchase Price |  | $ 51,600 |  |  |  |  |  |  |  |
Aggregate Annualized GAAP Rent |  | 6,800 |  |  |  |  |  |  |  |
Aggregate Debt Issued or Assumed |  | $ 28,800 |  |  |  |  |  |  |  |
Columbus, OH |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate Square Footage | ft² | 102,559 |  |  |  |  |  |  |  |  |
Lease Term | 6 years 10 months 24 days |  |  |  |  |  |  |  |  |
Aggregate Purchase Price | $ 17,300 |  |  |  |  |  |  |  |  |
Aggregate Annualized GAAP Rent | $ 1,700 |  |  |  |  |  |  |  |  |
Salt Lake City, UT |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate Square Footage | ft² | 102,028 |  |  |  |  |  | 107,062 |  |  |
Lease Term | 10 years 1 month 6 days |  |  |  |  |  | 6 years |  |  |
Aggregate Purchase Price | $ 20,500 |  |  |  |  |  | $ 17,000 |  |  |
Aggregate Annualized GAAP Rent | $ 3,000 |  |  |  |  |  | 1,400 |  |  |
Aggregate Debt Issued or Assumed |  |  |  |  |  |  | $ 9,900 |  |  |
Fort Lauderdale, FL |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate Square Footage | ft² |  |  |  |  |  | 119,224 |  |  |  |
Lease Term |  |  |  |  |  | 9 years |  |  |  |
Aggregate Purchase Price |  |  |  |  |  | $ 23,900 |  |  |  |
Aggregate Annualized GAAP Rent |  |  |  |  |  | 2,000 |  |  |  |
Aggregate Debt Issued or Assumed |  |  |  |  |  | $ 14,100 |  |  |  |
King of Prussia, PA |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Aggregate Square Footage | ft² |  |  |  |  | 103,334 |  |  |  |  |
Lease Term |  |  |  |  | 15 years |  |  |  |  |
Aggregate Purchase Price |  |  |  |  | $ 25,700 |  |  |  |  |
Acquisition Expenses |  |  |  |  | 200 |  |  |  |  |
Aggregate Annualized GAAP Rent |  |  |  |  | 2,200 |  |  |  |  |
Aggregate Debt Issued or Assumed |  |  |  |  | $ 14,800 |  |  |  |  |
Minimum |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Lease Term |  |  |  |  |  |  |  | 1 year | 1 year |
Maximum |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Lease Term |  |  |  |  |  |  |  | 11 years 3 months | 7 years 8 months 12 days |
New Fixed Rate Mortgage Notes Payable |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Noncash or part noncash acquisition, debt assumed |  |  |  |  |  |  |  | $ 54,900 |  |
New Fixed Rate Mortgage Notes Payable | Minimum | Philadelphia, PA |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  | 3.75% |  |  |  |  |  |  |
New Fixed Rate Mortgage Notes Payable | Maximum | Maitland, Florida |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  | 3.89% |  |  |  |  |  |  |  |
Interest Rate Swap |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Interest rate swap assumed |  |  |  | 1.80% |  |  |  |  |  |
Fixed interest rate risk exposure |  |  |  | 3.55% |  |  |  |  |  |
Interest Rate Swap | Conshohocken, Pennsylvania |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Noncash or part noncash acquisition, debt assumed |  |  |  | $ 11,200 |  |  |  |  |  |
Derivative asset |  |  |  | $ 40 |  |  |  | $ 300 |  |
Interest Rate Swap | New Fixed Rate Mortgage Notes Payable |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |
Debt instrument, interest rate, stated percentage |  |  |  |  |  |  |  | 3.545% |  |

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