Equity (Narrative) (Details)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended 30 Months Ended
Nov. 22, 2019
USD ($)
shares
Aug. 12, 2019
USD ($)
shares
May 09, 2019
USD ($)
$ / shares
shares
Jan. 02, 2019
USD ($)
$ / shares
shares
Jun. 28, 2018
USD ($)
$ / shares
shares
Jun. 27, 2017
USD ($)
$ / shares
shares
Apr. 14, 2017
USD ($)
investor
shares
Sep. 30, 2018
$ / shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Class of Stock [Line Items]                      
Number of institutional investors | investor             2        
Investor Unit conversion                   $ 919  
Amortization period                 4 years    
Percentage of taxable income including capital gains to be distributed to qualify as REIT                 100.00%    
Minimum percentage of taxable income excluding capital gains to be distributed to qualify as REIT                 90.00%    
Cash dividends declared                 $ 21,353 $ 10,939  
Dividends declared, per share (usd per share) | $ / shares                 $ 0.618 $ 0.60  
Distribution payable to noncontrolling interest                 $ 1,900   $ 1,900
Distribution payable to noncontrolling interest, per investor unit | $ / shares                 $ 0.15   $ 0.15
Dividends, ordinary income amount (in dollars per share) | $ / shares                 0.0699 0.1153  
Dividends, return of capital for tax reporting (in dollars per share) | $ / shares                 $ 0.5421 $ 0.4847  
IPO                      
Class of Stock [Line Items]                      
Proceeds from private placement offering           $ 45,000          
Investor units, price per unit (in dollars per share) | $ / shares           $ 20.00          
Common Stock                      
Class of Stock [Line Items]                      
Investor Unit conversion                   $ 1  
Common Stock | Initial Capitalization                      
Class of Stock [Line Items]                      
Number of institutional investors | investor             2        
Stock issued (in shares) | shares             2,875,000        
Investor Unit conversion             $ 57,500        
Common Stock | IPO                      
Class of Stock [Line Items]                      
Stock issued (in shares) | shares           10,250,000          
Proceeds from stock transaction           $ 205,000          
Common Stock | Director Compensation                      
Class of Stock [Line Items]                      
Stock issued during period, shares, issued for services | shares     40,000,000   40,000            
Stock issued during period, value, issued for services     $ 1,100   $ 800            
Common Stock | Public Offering                      
Class of Stock [Line Items]                      
Proceeds from stock transaction   $ 96,600                  
Number of shares issued in transaction | shares   3,450,000                  
Common Stock | Private Placement                      
Class of Stock [Line Items]                      
Proceeds from stock transaction $ 130,000 $ 168,000                  
Number of shares issued in transaction | shares 3,823,529 6,000,000                  
Payment of financing and stock issuance costs $ 5,000 $ 4,400                  
Common Stock | iStar Inc.                      
Class of Stock [Line Items]                      
Proceeds from stock transaction $ 117,300                    
Number of shares issued in transaction | shares 3,450,000                    
Common stock purchase plan, shares, purchased in period | shares                     3,400,000
Common stock purchase plan, amount purchased in period                     $ 73,400
Common Stock purchase plan, average share price (in dollars per share) | $ / shares                     $ 21.61
Number of shares purchased (in shares) | shares                     133,524
Common stock, amount purchased                     $ 2,200
Purchase of stock, average price per share (in dollars per share) | $ / shares                     $ 16.39
Percentage of ownership before transaction                 65.20%   65.20%
Common Stock | iStar Inc. | Initial Capitalization                      
Class of Stock [Line Items]                      
Stock issued (in shares) | shares             2,775,000        
Investor Unit conversion             $ 55,500        
Common Stock | iStar Inc. | IPO                      
Class of Stock [Line Items]                      
Stock issued (in shares) | shares           2,250,000          
Proceeds from private placement offering           $ 45,000          
Retained Earnings / Accumulated (Deficit)                      
Class of Stock [Line Items]                      
Cash dividends declared                 $ 21,353 10,939  
Dividends declared, per share (usd per share) | $ / shares                 $ 0.618    
SAFE | iStar Inc. | Maximum                      
Class of Stock [Line Items]                      
Common stock voting rights, investor units voting power threshold                 41.90%   41.90%
Performance Shares                      
Class of Stock [Line Items]                      
Ownership percentage after transaction               85.00%      
Capital appreciation aggregate distribution, percent               15.00%      
Awards with aggregate intrinsic value                 $ 1,500   $ 1,500
Performance Shares | Equity Plan | Common Stock                      
Class of Stock [Line Items]                      
Share price (in dollars per share) | $ / shares     $ 27.19   $ 19.13            
Performance Shares | Equity Plan | Maximum | Common Stock                      
Class of Stock [Line Items]                      
Share price (in dollars per share) | $ / shares               $ 35.00      
Capital appreciation aggregate distribution, percent                 25.00%   25.00%
Awards subject to forfeiture based on continuing service conditions, percent                 75.00%   75.00%
Performance Shares | Equity Plan | Minimum | Common Stock                      
Class of Stock [Line Items]                      
Share price (in dollars per share) | $ / shares               $ 25.00      
Stock Price Hurdle One | Performance Shares | Equity Plan | Common Stock                      
Class of Stock [Line Items]                      
Share price (in dollars per share) | $ / shares                 $ 25.00   $ 25.00
Stock Price Hurdle Two | Performance Shares | Equity Plan | Common Stock                      
Class of Stock [Line Items]                      
Share price (in dollars per share) | $ / shares                 27.50   27.50
Stock Price Hurdle Three | Performance Shares | Equity Plan | Common Stock                      
Class of Stock [Line Items]                      
Share price (in dollars per share) | $ / shares                 30.00   30.00
Stock Price Hurdle Four | Performance Shares | Equity Plan | Common Stock                      
Class of Stock [Line Items]                      
Share price (in dollars per share) | $ / shares                 32.5   32.5
Stock Price Hurdle Five | Performance Shares | Equity Plan | Common Stock                      
Class of Stock [Line Items]                      
Share price (in dollars per share) | $ / shares                 $ 35.00   35.00
Manager | Performance Shares                      
Class of Stock [Line Items]                      
Aggregate compensation cost                 $ 1,400    
General and Administrative Expense | 2017 Equity Incentive Plan                      
Class of Stock [Line Items]                      
Share-based payment arrangement, expense                 1,200 800  
General and Administrative Expense | Restricted Stock Units (RSUs) | 2017 Equity Incentive Plan                      
Class of Stock [Line Items]                      
Investor Unit conversion                 $ 500    
Share price (in dollars per share) | $ / shares                 $ 19.15   $ 19.15
Cost not yet recognized, amount                 $ 300   $ 300
Capital shares reserved for future issuance (in shares) | shares                 762,500   762,500
Stock issued during period, shares, issued for services | shares                 25,000    
General and Administrative Expense | Manager | Performance Shares | Equity Plan | Common Stock                      
Class of Stock [Line Items]                      
Aggregate compensation cost                 $ 400 $ 100  
iStar Inc.                      
Class of Stock [Line Items]                      
Investor unit conversion       $ 250,000              
Investor units, price per unit (in dollars per share) | $ / shares       $ 20.00              
Number of shares issued in transaction | shares       12,500,000