Earnings Per Share (Earnings Allocable to Common Shares) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator for basic earnings per share:
Income (loss) from continuing operations attributable to iStar Inc. and allocable to common shareholders	$ 26,809	$ (31,868)
Income from discontinued operations	0	4,766
Net income (loss) allocable to common shareholders	26,809	(27,102)
Numerator for diluted earnings per share:
Income (loss) from continuing operations attributable to iStar Inc. and allocable to common shareholders	29,059	(31,868)
Income from discontinued operations	0	4,766
Net income (loss) attributable to iStar Inc. and allocable to common shareholders	$ 29,059	$ (27,102)
Denominator for basic and diluted earnings per share:
Weighted average common shares outstanding for basic earnings per common share (in shares)	67,913	72,065
Add: Effect of assumed shares issued under treasury stock method for restricted stock units (in shares)	122	0
Weighted average common shares outstanding for diluted earnings per common share (in shares)	83,670	72,065
Basic earnings per common share:
Income (loss) from continuing operations attributable to iStar Inc. and allocable to common shareholders (in dollars per share)	$ 0.39	$ (0.44)
Income (loss) from discontinued operations (in dollars per share)	0.00	0.06
Net income (loss) attributable to iStar Inc. and allocable to common shareholders (in dollars per share)	0.39	(0.38)
Diluted earnings per common share:
Income (loss) from continuing operations attributable to iStar Inc. and allocable to common shareholders (in dollars per share)	0.35	(0.44)
Income from discontinued operations (in dollars per share)	0.00	0.06
Net income (loss) attributable to iStar Inc. and allocable to common shareholders (in dollars per share)	$ 0.35	$ (0.38)
Preferred Stock Series J
Denominator for basic and diluted earnings per share:
Add: Effect of series J convertible perpetual preferred stock (in shares)	15,635	0