Related Party Transactions (Narrative) (Details) $ / shares in Units, $ in Thousands, ft² in Millions		1 Months Ended								3 Months Ended		9 Months Ended
	Aug. 10, 2022 USD ($) shares	Sep. 30, 2023 USD ($)	Jul. 31, 2022 USD ($)	Jun. 30, 2022 USD ($) director	Apr. 30, 2022 USD ($)	Mar. 31, 2022 USD ($) director lease property	Feb. 28, 2022 USD ($) director shares	Nov. 30, 2021 USD ($) director	Jun. 30, 2021 USD ($) ft² agreement director	Mar. 31, 2023 USD ($) employee $ / shares shares	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)
Related Party Transaction [Line Items]
Financing Receivable, after Allowance for Credit Loss, Related Party, Type		Related party										Related party
Management fee expense												$ 5,199	$ 14,950
Ground lease acquisition purchase price												170,194	515,618
Future funding obligation, amount		$ 283,600										283,600
Number of new Ground Leases entered into | lease						3
Land
Related Party Transaction [Line Items]
Payments to acquire land						$ 28,500
Land and Related Ground Lease
Related Party Transaction [Line Items]
Leasehold improvement allowance, funded amount		12,700										12,700
Office space development property
Related Party Transaction [Line Items]
Number of square feet | ft²									1.1
Proceeds from sale of acquisition right under purchase option agreement		300
Purchase price of property under purchase option agreement									$ 215,000
Office space development property | Other expense
Related Party Transaction [Line Items]
Loss on sale of acquisition right under purchase option agreement		$ 1,900
Mixed-use property
Related Party Transaction [Line Items]
Ground lease, additional construction, funding commitment				$ 35,000
Caret Units
Related Party Transaction [Line Items]
Number of units sold | shares							108,571
Number of shares to be sold under purchase commitment related to merger | shares							28,571
Expected proceeds from sale of shares under purchase commitment							$ 5,000
Number of independent directors affiliated with an existing shareholder investing in redeemable noncontrolling interest | director							1
Period in which the entity is obligated to provide a public market listing							2 years
Caret Units | MSD Partners
Related Party Transaction [Line Items]
Number of shares to be sold under purchase commitment related to merger | shares	100,000
Expected proceeds from sale of shares under purchase commitment	$ 20,000
Existing third-party Caret unit
Related Party Transaction [Line Items]
Number of shares to be sold under purchase commitment related to merger | shares										22,500
Expected proceeds from sale of shares under purchase commitment										$ 4,500
Affiliated entity | iStar Inc.
Related Party Transaction [Line Items]
Management fee paid with common stock, period of restriction from selling stock										2 years
Management fee, percent, threshold one										1.00%
Management fee, percent, threshold two										1.25%
Management fee, percent, threshold three										1.375%
Management fee, percent, threshold four										1.50%
Termination fee, percent of prior years management fee										3.00%
Incentive fee										$ 0
Ground lease acquisition purchase price			$ 36,400		$ 9,000
Payment to acquire purchase option agreement									$ 1,200
Payments to acquire land						$ 122,000
Number of land properties acquired | property						3
Payment to terminate a real estate purchase option						$ 300
Affiliated entity | iStar Inc. | General and Administrative Expense
Related Party Transaction [Line Items]
Management fee expense											$ 5,300	5,200	15,000
Reimbursed operating and administrative expenses											$ 3,100	$ 3,100	$ 9,400
Affiliated entity | iStar Inc. | Land and Related Ground Lease
Related Party Transaction [Line Items]
Number of agreements entered into to acquire land and related Ground Lease | agreement									2
Purchase price per agreement for acquisition of land and related Ground Lease, subject to certain conditions being met								$ 33,300	$ 42,000
Multiple required by seller that may trigger payment of additional consideration								1.25	1.25
Percentage of required seller return on investment that may trigger payment of additional consideration								12.00%	9.00%
Future funding obligation, amount								$ 51,800
Affiliated entity | Minimum | iStar Inc.
Related Party Transaction [Line Items]
Management fee, shareholders' equity, incremental threshold amount two										1,500,000
Management fee, shareholders' equity, incremental threshold amount three										3,000,000
Management fee, shareholders' equity, incremental threshold amount four										5,000,000
Affiliated entity | Maximum | iStar Inc.
Related Party Transaction [Line Items]
Management fee, shareholders' equity, incremental threshold amount one										1,500,000
Management fee, shareholders' equity, incremental threshold amount two										3,000,000
Management fee, shareholders' equity, incremental threshold amount three										$ 5,000,000
Affiliated entity | Maximum | iStar Inc. | Land and Related Ground Lease
Related Party Transaction [Line Items]
Real estate, leasehold improvement allowance									$ 83,000
Affiliated entity | IPO | iStar Inc.
Related Party Transaction [Line Items]
Share price (in dollars per share) | $ / shares										$ 20.00
Director
Related Party Transaction [Line Items]
Number of directors with indirect ownership in Ground lease tenant. | director						1
Number of independent directors affiliated with an existing shareholder participating in or related to a particular project or transaction | director							1
iStar Inc.
Related Party Transaction [Line Items]
Ground lease acquisition purchase price			$ 36,400
iStar Inc. | Land and Related Ground Lease
Related Party Transaction [Line Items]
Number of independent directors affiliated with an existing shareholder participating in or related to a particular project or transaction | director								1	1
iStar Shareholder Affiliate | Mixed-use property
Related Party Transaction [Line Items]
Number of directors affiliated with shareholder having indirect ownership in venture | director				1
Leasehold Loan Fund
Related Party Transaction [Line Items]
Ownership percentage		53.00%										53.00%
Leasehold Loan Fund | Life Science Office Property Development
Related Party Transaction [Line Items]
Loan commitment received to fund a recapitalization project							$ 130,000
Additional consideration paid							$ 9,000
Leasehold Loan Fund | Mixed-use property
Related Party Transaction [Line Items]
Loan commitment received to fund a recapitalization project				$ 105,000
Additional consideration paid				$ 5,000
iStar Inc.
Related Party Transaction [Line Items]
Number of years as active real estate investor										20 years
Number of agreements entered into to acquire land and related Ground Lease | agreement									2
iStar Inc. | MSD Partners
Related Party Transaction [Line Items]
Number of shares to be sold under purchase commitment related to merger | shares	5,405,406									5,405,406
Expected proceeds from sale of shares under purchase commitment	$ 200,000
Safehold, Inc. (Old SAFE)
Related Party Transaction [Line Items]
Number of employees | employee										0
Safehold, Inc. (Old SAFE) | Caret Units
Related Party Transaction [Line Items]
Number of units sold | shares							108,571
Percentage of authorized shares sold							1.08%
Number of shares to be sold under purchase commitment related to merger | shares							28,571
Percentage of authorized shares under commitment to be purchased							0.29%
Expected proceeds from sale of shares under purchase commitment							$ 5,000
Number of independent directors affiliated with an existing shareholder investing in redeemable noncontrolling interest | director							1
Period in which the entity is obligated to provide a public market listing							2 years
MSD Partners | Caret Units
Related Party Transaction [Line Items]
Number of shares to be sold under purchase commitment related to merger | shares										100,000
Expected proceeds from sale of shares under purchase commitment										$ 20,000