Other Investments (Narrative) (Details)	6 Months Ended
	Jun. 30, 2015 USD ($) Investee	Jun. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of Net Lease Assets Under Term Loan | Investee	1
Distributions from operations of equity method investments	$ 7,843,000	$ 10,939,000
Equity method investments	289,500,000		$ 354,119,000
Proceeds from Sale of Available-for-sale Securities, Equity	7,300,000
Available-for-sale Securities, Gross Realized Gain (Loss)	2,500,000
Marina Palms
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 40,295,000		30,677,000
MIRELF III
Schedule of Equity Method Investments [Line Items]
iStar's ownership percentage	32.90%
MIRELF III AIV
Schedule of Equity Method Investments [Line Items]
iStar's ownership percentage	32.90%
Madison GP1 Investors LP
Schedule of Equity Method Investments [Line Items]
iStar's ownership percentage	29.50%
Net Lease Venture
Schedule of Equity Method Investments [Line Items]
Distributions from operations of equity method investments	$ 61,200,000
Equity method investments	$ 70,409,000		125,361,000
Madison International Real Estate Fund IILP [Member]
Schedule of Equity Method Investments [Line Items]
iStar's ownership percentage	29.50%
Net Lease Asset One | Net Lease Venture
Schedule of Equity Method Investments [Line Items]
Net proceeds from sales of real estate		$ 93,700,000
Land | Marina Palms
Schedule of Equity Method Investments [Line Items]
iStar's ownership percentage	47.50%
Equity method investment, preferred interest	$ 10,000,000
Total assets	283,600,000		265,700,000
Land | Real Estate Equity Investment Two [Member]
Schedule of Equity Method Investments [Line Items]
iStar's ownership percentage		85.70%
Equity method investments	8,300,000		9,400,000
Loans Receivable, Commitments, Related Party		$ 45,700,000
Land | Other real estate equity investments
Schedule of Equity Method Investments [Line Items]
Equity method investments	64,400,000		66,100,000
Net Lease
Schedule of Equity Method Investments [Line Items]
Net proceeds from sales of real estate		$ 7,800,000
Net Lease | Net Lease Venture
Schedule of Equity Method Investments [Line Items]
iStar's ownership percentage		51.90%
Partners' capital account, contributions		$ 500,000,000
Equity method investment, related party ownership percentage		0.60%
Equity method investment, related party promote fee percentage		50.00%
Equity method investment, partner ownership percentage		47.50%
Net proceeds from sales of real estate		$ 93,700,000
Total assets	382,200,000		348,100,000
Operating Properties | Other real estate equity investments
Schedule of Equity Method Investments [Line Items]
Equity method investments	$ 11,400,000		$ 13,200,000
Minimum | Other real estate equity investments
Schedule of Equity Method Investments [Line Items]
iStar's ownership percentage	16.00%
Maximum | Other real estate equity investments
Schedule of Equity Method Investments [Line Items]
iStar's ownership percentage	76.00%
Loans Receivable and Other Lending Investments, Net [Member] | Land | Real Estate Equity Investment Two [Member]
Schedule of Equity Method Investments [Line Items]
Loans Receivable, Related Party	$ 31,200,000
Net Lease
Schedule of Equity Method Investments [Line Items]
Debt Instrument, Maturity Date	10 years
Debt instrument, face amount	$ 120,000,000.0