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Real Estate and Intangible Assets - Additional Information (Detail) $ in Thousands |  | 3 Months Ended | 6 Months Ended |  |
--- | --- | --- | --- | --- | ---
May 26, 2016 USD ($) ft² | Jun. 30, 2018 USD ($) ft² property | Jun. 30, 2017 USD ($) ft² property | Jun. 30, 2018 USD ($) ft² property | Jun. 30, 2017 USD ($) ft² property | Jun. 22, 2018 | Jun. 22, 2017
Real Estate Properties [Line Items] |  |  |  |  |  |  |
Number of properties acquired | property |  | 1 | 1 | 1 | 1 |  |
Purchase Price |  |  |  | $ 14,341 |  |  |
Change in unrealized gain related to interest rate hedging instruments, net |  | $ 289 | $ 179 | $ 783 | $ 179 |  |
Number of leased properties | property |  |  |  | 1 | 1 |  |
Total amortization expense related to lease intangible assets |  | 4,300 | 3,500 | $ 8,600 | $ 7,000 |  |
Amortization related to below-market lease |  | 500 | 300 | 1,000 | 700 |  |
Above market leases |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |
Amortization related to above-market lease |  | 200 | 100 | 500 | 300 |  |
Building and Tenant Improvements |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |
Real estate depreciation expense |  | $ 7,500 | $ 6,400 | $ 14,800 | $ 12,800 |  |
Series of Property Acquisitions |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |
Aggregate Square Footage Sold | ft² |  | 127,444 | 60,016 | 127,444 | 60,016 |  |
Purchase Price |  |  |  | $ 14,341 | $ 15,697 |  |
Mortgage loans on real estate, new mortgage loans |  |  |  | $ 0 | $ 11,179 |  |
Lease Term |  |  |  | 9 years 9 months 18 days | 8 years 6 months |  |
Annualized GAAP Rent |  |  |  | $ 1,087 | $ 1,680 |  |
Acquisition Expenses |  |  |  | 91 | 247 |  |
Conshohocken, Pennsylvania |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |
Aggregate Square Footage Sold | ft² | 60,016 |  |  |  |  |  |
Purchase Price | $ 15,700 |  |  |  |  |  |
Mortgage loans on real estate, new mortgage loans | $ 11,200 |  |  |  |  |  |
Lease Term | 8 years 6 months |  |  |  |  |  |
Annualized GAAP Rent | $ 1,700 |  |  |  |  |  |
Stated interest rate (as percent) |  |  |  |  |  | 1.80% | 1.80%
Asset Acquisitions |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |
Purchase Price |  |  |  |  | 15,697 |  |
Interest rate swap |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |
Change in unrealized gain related to interest rate hedging instruments, net |  | $ 192 | $ 179 | 313 | 179 |  |
Interest rate swap | Asset Acquisitions |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |
Liabilities Assumed |  |  |  | 0 | $ 42 |  |
Change in unrealized gain related to interest rate hedging instruments, net |  |  |  | $ 700 |  |  |
LIBOR | Interest rate swap | Conshohocken, Pennsylvania |  |  |  |  |  |  |
Real Estate Properties [Line Items] |  |  |  |  |  |  |
Derivative rate (as a percent) |  |  |  |  |  |  | 3.55%

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- 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=98514028&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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