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Other Investments (Narrative) (Details) |  |  | 1 Months Ended | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Jun. 27, 2017 USD ($) | Apr. 14, 2017 USD ($) | Apr. 30, 2017 USD ($) property | Dec. 31, 2016 USD ($) | Jun. 30, 2017 USD ($) unit | Jun. 30, 2016 USD ($) | Jun. 30, 2017 USD ($) unit | Jun. 30, 2016 USD ($) | Mar. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Net proceeds from sales of other investments |  |  |  |  |  |  |  | $ 0 | $ 39,810,000 |
Earnings from equity method investments |  |  |  |  |  | $ 5,515,000 | $ 39,447,000 | 11,217,000 | 47,714,000 |
Acquisitions of real estate assets |  |  |  |  |  |  |  | 0 | 3,915,000 |
Net proceeds from sales of real estate |  |  |  |  |  |  |  | 154,291,000 | 247,956,000 |
Carrying value of assets |  |  |  |  | $ 4,825,514,000 | 4,914,755,000 |  | 4,914,755,000 |  |
Gain sale of properties | [1] |  |  |  |  | $ 844,000 | 43,484,000 | $ 8,954,000 | 53,943,000 |
Noncontrolling interest, ownership percentage by parent |  |  |  |  |  | 95.70% |  | 95.70% |  |
Equity method investments, carrying value |  |  |  |  | 214,406,000 | $ 276,821,000 |  | $ 276,821,000 |  |
Contributions |  |  |  |  |  |  |  | 139,139,000 | 8,283,000 |
Cost method investments |  |  |  |  | 1,400,000 | 900,000 |  | 900,000 |  |
Other real estate equity investments | Operating Properties |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Equity method investments, carrying value |  |  |  |  | 3,600,000 | 7,900,000 |  | 7,900,000 |  |
Contributions |  |  |  |  | 7,000,000 |  |  |  |  |
Loan commitments |  |  |  |  | 27,000,000 |  |  |  |  |
Loans receivable, carrying value |  |  |  |  | 22,700,000 | 23,600,000 |  | 23,600,000 |  |
Interest income |  |  |  |  |  | 500,000 |  | 900,000 |  |
Other real estate equity investments | Land & Development |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Equity method investments, carrying value |  |  |  |  | 49,600,000 | $ 55,200,000 |  | $ 55,200,000 |  |
Other real estate equity investments | Minimum |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
iStar's ownership percentage |  |  |  |  |  | 20.00% |  | 20.00% |  |
Other real estate equity investments | Maximum |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
iStar's ownership percentage |  |  |  |  |  | 85.00% |  | 85.00% |  |
Oak Hill Funds |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Earnings from equity method investments |  |  |  |  |  |  | 500,000 |  | 3,700,000 |
Net lease venture |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
iStar's ownership percentage |  |  |  |  |  | 51.90% |  | 51.90% |  |
Partners' capital account, contributions (up to) |  |  |  |  |  | $ 500,000,000 |  | $ 500,000,000 |  |
Equity method investment, related party ownership percentage |  |  |  |  |  | 0.60% |  | 0.60% |  |
Equity method investment, related party promote fee percentage |  |  |  |  |  | 50.00% |  | 50.00% |  |
Equity method investment, partner ownership percentage |  |  |  |  |  | 47.50% |  | 47.50% |  |
Acquisitions of real estate assets |  |  |  |  |  |  |  | $ 59,000,000 |  |
Net proceeds from sales of real estate |  |  |  |  |  |  |  | 6,200,000 |  |
Financing derecognized after sale |  |  |  |  |  |  |  | 18,900,000 |  |
Total assets carrying value |  |  |  |  | 511,300,000 | $ 626,500,000 |  | 626,500,000 |  |
Net lease venture | Other income |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Management fees revenue |  |  |  |  |  | $ 500,000 | 400,000 | $ 900,000 | 800,000 |
Marina Palms |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
iStar's ownership percentage |  |  |  |  |  | 47.50% |  | 47.50% |  |
Total assets carrying value |  |  |  |  | $ 201,800,000 | $ 52,700,000 |  | $ 52,700,000 |  |
Number of units | unit |  |  |  |  |  | 468 |  | 468 |  |
Marine Palms North Tower |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Number of units | unit |  |  |  |  |  | 234 |  | 234 |  |
Number of units remaining for sale | unit |  |  |  |  |  | 1 |  | 1 |  |
Marine Palms South Tower |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Number of units | unit |  |  |  |  |  | 234 |  | 234 |  |
Percentage of units pre-sold |  |  |  |  |  |  |  | 84.00% |  |
Newly formed unconsolidated entity |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
iStar's ownership percentage |  |  |  |  | 50.00% |  |  |  |  |
Safety, Income and Growth, Inc. |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
iStar's ownership percentage |  |  |  |  |  | 28.00% |  | 28.00% |  |
Contributions by majority shareholders |  |  | $ 57,500,000 |  |  |  |  |  |  |
Carrying value of assets |  |  |  | $ 161,100,000 |  |  |  |  |  |
Gain sale of properties |  |  |  | 123,400,000 |  |  |  |  |  |
Safety, Income and Growth, Inc. | IPO |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Payments of Stock Issuance Costs |  | $ 16,600,000 |  |  |  |  |  |  |  |
Offering costs |  | 25,000,000 |  |  |  |  |  |  |  |
Safety, Income and Growth, Inc. | Private Placement |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Proceeds from issuance initial public offering |  | 205,000,000 |  |  |  |  |  |  |  |
Proceeds from issuance of private placement |  | $ 45,000,000 |  |  |  |  |  |  |  |
Wholly-owned Subsidiary | Other real estate equity investments |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Net proceeds from sales of other investments |  |  |  |  |  |  |  |  | 39,800,000 |
Gain on sale of equity method investment |  |  |  |  |  |  |  |  | 31,500,000 |
Gain on sale of equity method investment attributable to noncontrolling interest |  |  |  |  |  |  |  |  | 10,100,000 |
Wholly-owned Subsidiary | Safety, Income and Growth, Inc. |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Management fee, percent of equity below threshold |  |  |  |  |  |  |  | 1.00% |  |
Management fee, percent of equity above threshold |  |  |  |  |  |  |  | 0.75% |  |
Management fee, shareholders' equity threshold amount |  |  |  |  |  | $ 2,500,000,000.0 |  | $ 2,500,000,000.0 |  |
Ground Net Lease Business | Safety, Income and Growth, Inc. |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Net proceeds from sales of real estate |  |  | 113,000,000 | $ 113,000,000 |  |  |  |  |  |
Number of properties | property |  |  |  | 12 |  |  |  |  |  |
Payments to acquire equity method investments |  |  | $ 55,500,000 | $ 55,500,000 |  |  |  |  |  |
Noncontrolling interest (as a percent) |  |  | 49.00% |  |  |  |  |  |  |
Noncontrolling interest, ownership percentage by parent |  |  | 51.00% |  |  |  |  |  |  |
2017 Secured Financing |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Debt instrument, face amount |  |  | $ 227,000,000.0 |  |  | 227,000,000.0 |  | 227,000,000.0 |  | $ 227,000,000.0
Real estate equity investments |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Earnings from equity method investments |  |  |  |  |  | 5,155,000 | 34,724,000 | 10,610,000 | 42,189,000 |
Equity method investments, carrying value |  |  |  |  | $ 181,056,000 | 249,582,000 |  | 249,582,000 |  |
Real estate equity investments | Safety, Income and Growth, Inc. |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Earnings from equity method investments |  |  |  |  |  |  | 0 | 48,000 | 0 |
Equity method investments, carrying value |  |  |  |  | 0 | 50,287,000 |  | 50,287,000 |  |
Real estate equity investments | Other real estate equity investments |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Earnings from equity method investments |  |  |  |  |  | 2,892,000 | 28,600,000 | 4,249,000 | 26,898,000 |
Equity method investments, carrying value |  |  |  |  | 53,202,000 | 63,107,000 |  | 63,107,000 |  |
Real estate equity investments | Net lease venture |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Earnings from equity method investments |  |  |  |  |  | 1,032,000 | 944,000 | 2,013,000 | 1,890,000 |
Equity method investments, carrying value |  |  |  |  | 92,669,000 | 128,997,000 |  | 128,997,000 |  |
Real estate equity investments | Marina Palms |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Earnings from equity method investments |  |  |  |  |  | 1,183,000 | $ 5,180,000 | 4,300,000 | $ 13,401,000 |
Equity method investments, carrying value |  |  |  |  | $ 35,185,000 | 7,191,000 |  | $ 7,191,000 |  |
Real estate equity investments | Safety, Income and Growth, Inc. | Safety, Income and Growth, Inc. |  |  |  |  |  |  |  |  |  |
Schedule of Equity Method Investments [Line Items] |  |  |  |  |  |  |  |  |  |
Earnings from equity method investments |  |  |  |  |  | $ 48,000 |  |  |  |
[1] | Income from sales of real estate represents gains from sales of real estate that do not qualify as discontinued operations.

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