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Other Investments (Schedule of Other Investments) (Details) - USD ($) $ in Thousands		12 Months Ended
	Jan. 02, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Schedule of Equity Method Investments [Line Items]
Other investments		$ 304,275	$ 321,241		$ 397,110
Equity in Earnings (Losses)		(5,007)	13,015	$ 77,349
Additional cash investment in equity method investment		94,578	224,219	58,197
Net proceeds from sale of equity method investment		0	0	43,936
Distribution from equity method investments		18,133	42,059	48,732
Net Lease Venture
Schedule of Equity Method Investments [Line Items]
Additional cash investment in equity method investment			49,200
Other Strategic Investments
Schedule of Equity Method Investments [Line Items]
Other investments		7,516	13,618
Equity in Earnings (Losses)		(9,373)	1,410	9,907
Impairment on foreign equity method investment		10,000
Real Estate Investment
Schedule of Equity Method Investments [Line Items]
Carrying value		296,759	307,623
Equity in Earnings (Losses)		4,366	11,605	67,442
Real Estate Investment \| Safety, Income and Growth, Inc.
Schedule of Equity Method Investments [Line Items]
Carrying value		149,589	83,868
Equity in Earnings (Losses)		4,711	551	0
Real Estate Investment \| iStar Net Lease II LLC (Net Lease Venture II)
Schedule of Equity Method Investments [Line Items]
Carrying value		16,215	0
Equity in Earnings (Losses)		(333)	0	0
Real Estate Investment \| Net Lease Venture
Schedule of Equity Method Investments [Line Items]
Carrying value		0	121,139
Equity in Earnings (Losses)		4,100	4,534	3,567
Real Estate Investment \| Other real estate equity investments
Schedule of Equity Method Investments [Line Items]
Carrying value		130,955	102,616
Equity in Earnings (Losses)		(4,112)	$ 6,520	63,875
Net proceeds from sale of equity method investment				39,800
Impairment on foreign equity method investment		$ 6,100
Gain on sale recognized earnings				31,500
Distribution from equity method investments				11,600
Real Estate Investment \| Other real estate equity investments \| Noncontrolling Interests
Schedule of Equity Method Investments [Line Items]
Gain on sale recognized earnings				$ 10,100
Subsequent Event \| Real Estate Investment \| Safety, Income and Growth, Inc.
Schedule of Equity Method Investments [Line Items]
Additional cash investment in equity method investment	$ 250,000