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Other Investments (Schedule of Other Investments) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Schedule of Equity Method Investments [Line Items]
Total	$ 302,318		$ 302,318		$ 321,241
Earnings (losses) from equity method investments	(635)	$ 2,461	(4,581)	$ 13,677
Impairment on foreign equity method investment			10,000
Other strategic investments
Schedule of Equity Method Investments [Line Items]
Total	7,268		7,268		13,618
Earnings (losses) from equity method investments	652	610	(9,521)	1,216
Real estate equity investments
Schedule of Equity Method Investments [Line Items]
Equity method investments, carrying value	295,050		295,050		307,623
Earnings (losses) from equity method investments	(1,287)	1,851	4,940	12,461
Real estate equity investments \| Net Lease Venture
Schedule of Equity Method Investments [Line Items]
Equity method investments, carrying value	0		0		121,139
Earnings (losses) from equity method investments	0	962	4,100	2,975
Real estate equity investments \| Safety, Income and Growth, Inc.
Schedule of Equity Method Investments [Line Items]
Equity method investments, carrying value	150,533		150,533		83,868
Earnings (losses) from equity method investments	775	340	2,927	388
Real estate equity investments \| Other real estate equity investments
Schedule of Equity Method Investments [Line Items]
Equity method investments, carrying value	144,517		144,517		$ 102,616
Earnings (losses) from equity method investments	$ (2,062)	$ 549	$ (2,087)	$ 9,098