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Subsequent Events - Additional Information (Details) $ in Thousands |  |  |  |  |  |  | 2 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Feb. 08, 2019 USD ($) tenant | Jan. 31, 2019 USD ($) | Dec. 27, 2018 USD ($) | Oct. 27, 2017 | Jul. 31, 2017 USD ($) | Jul. 07, 2017 USD ($) | Feb. 13, 2019 USD ($) shares | Dec. 31, 2018 USD ($) shares | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) | Jan. 11, 2019 USD ($)
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gain on sale of real estate, net |  |  |  |  |  |  |  | $ 2,763 | $ 3,993 | $ 242 |
Purchase price |  |  |  |  |  |  |  | $ 63,245 | $ 132,157 |  |
Maitland, Florida |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase price |  |  |  |  | $ 51,600 |  |  |  |  |  |
Lease Term |  |  |  |  | 8 years 7 months 6 days |  |  |  |  |  |
Debt issued or assumed |  |  |  |  | $ 28,800 |  |  |  |  |  |
Stated interest rate (as a percent) |  |  |  |  | 3.89% |  |  |  |  |  |
Maitland, Florida | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Gross proceeds from sale of property |  | $ 6,900 |  |  |  |  |  |  |  |  |
Gain on sale of real estate, net |  | $ 3,000 |  |  |  |  |  |  |  |  |
Philadelphia, Pennsylvania |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase price |  |  |  |  |  | $ 27,100 |  |  |  |  |
Lease Term |  |  |  |  |  | 15 years 4 months 24 days |  |  |  |  |
Debt issued or assumed |  |  |  |  |  | $ 14,900 |  |  |  |  |
Stated interest rate (as a percent) |  |  |  |  |  | 3.75% |  |  |  |  |
Philadelphia, Pennsylvania | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase price | $ 2,700 |  |  |  |  |  |  |  |  |  |
Number of tenants | tenant | 1 |  |  |  |  |  |  |  |  |  |
Lease Term | 15 years |  |  |  |  |  |  |  |  |  |
Lake Mary, Florida |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Purchase price |  |  | $ 18,700 |  |  |  |  |  |  |  |
Lease Term |  |  | 11 years |  |  |  |  |  |  |  |
Lake Mary, Florida | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt issued or assumed | $ 10,600 |  |  |  |  |  |  |  |  |  |
Fixed rate mortgage loans |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rate (as a percent) |  |  |  |  |  |  |  | 5.75% |  |  |
Fixed rate mortgage loans | Lake Mary, Florida | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Stated interest rate (as a percent) | 4.70% |  |  |  |  |  |  |  |  |  |
Debt instrument term | 7 years |  |  |  |  |  |  |  |  |  |
Fixed rate mortgage loans debt extended |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument term |  |  |  |  |  |  |  | 3 years |  |  |
Fixed rate mortgage loans debt extended | Lake Mary, Florida | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Debt instrument term | 3 years |  |  |  |  |  |  |  |  |  |
LIBOR |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on LIBOR (as percent) |  |  |  | 2.75% |  |  |  |  |  |  |
LIBOR | Fixed rate mortgage loans | Lake Mary, Florida | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on LIBOR (as percent) | 1.80% |  |  |  |  |  |  |  |  |  |
LIBOR | Variable rate mortgage loans | Lake Mary, Florida | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Spread on LIBOR (as percent) | 1.80% |  |  |  |  |  |  |  |  |  |
2019 Universal Shelf | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Universal registration statement, amount authorized |  |  |  |  |  |  |  |  |  |  | $ 500,000
Series A and B Preferred Stock ATM Programs | Series A and B Preferred Stock | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of shares sold (in shares) | shares |  |  |  |  |  |  | 0 |  |  |  |
Cantor Fitzgerald & Co | Series D Preferred Stock ATM Program | Series D Preferred Stock |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net proceeds from sale of shares |  |  |  |  |  |  |  | $ 2,200 |  |  |
Number of shares sold (in shares) | shares |  |  |  |  |  |  |  | 100,000 |  |  |
Cantor Fitzgerald & Co | Series D Preferred Stock ATM Program | Series D Preferred Stock | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Number of shares sold (in shares) | shares |  |  |  |  |  |  | 0 |  |  |  |
Cantor Fitzgerald & Co | Common Stock | Common Stock ATM Program |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net proceeds from sale of shares |  |  |  |  |  |  |  | $ 16,100 |  |  |
Number of shares sold (in shares) | shares |  |  |  |  |  |  |  | 800,000 |  |  |
Cantor Fitzgerald & Co | Common Stock | Common Stock ATM Program | Subsequent event |  |  |  |  |  |  |  |  |  |  |
Subsequent Event [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net proceeds from sale of shares |  |  |  |  |  |  | $ 3,400 |  |  |  |
Number of shares sold (in shares) | shares |  |  |  |  |  |  | 179,785 |  |  |  |

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