Other Investments - Safehold Inc. (Details) $ / shares in Units, shares in Millions		1 Months Ended					3 Months Ended
	Jan. 02, 2019 director	Mar. 31, 2020 USD ($) multiple shares	Feb. 28, 2019	Jan. 31, 2019 USD ($) $ / shares shares	May 31, 2018 USD ($) office_building	Oct. 31, 2017 USD ($)	Mar. 31, 2020 USD ($) multiple	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Aug. 31, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Number of limited partnership units purchased (in shares) | shares				12.5
Investor units, purchase price per unit (in dollars per share) | $ / shares				$ 20.00
Additional cash investment in equity method investment				$ 250,000,000.0			$ 118,991,000	$ 260,297,000
Restriction period on common stock received as payment							2 years
Management agreement, termination fee as multiple of prior year management fee | multiple		3					3
Commitment to provide loan to lessee									$ 150,000,000.0
Fee percent of SAFE Equity up to $1.5 billion
Schedule of Equity Method Investments [Line Items]
Management fee as percent of equity							1.00%
Fee percent of SAFE Equity up to $1.5 billion | Maximum
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount		$ 1,500,000,000					$ 1,500,000,000
Fee percent of SAFE Equity between $1.5 billion and $3.0 billion
Schedule of Equity Method Investments [Line Items]
Management fee as percent of equity							1.25%
Fee percent of SAFE Equity between $1.5 billion and $3.0 billion | Minimum
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount		1,500,000,000					$ 1,500,000,000
Fee percent of SAFE Equity between $1.5 billion and $3.0 billion | Maximum
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount		3,000,000,000.0					$ 3,000,000,000.0
Fee percent of SAFE Equity between $3.0 billion and $5.0 billion
Schedule of Equity Method Investments [Line Items]
Management fee as percent of equity							1.375%
Fee percent of SAFE Equity between $3.0 billion and $5.0 billion | Minimum
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount		3,000,000,000.0					$ 3,000,000,000.0
Fee percent of SAFE Equity between $3.0 billion and $5.0 billion | Maximum
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount		5,000,000,000.0					$ 5,000,000,000.0
Fee percent of SAFE Equity over $5.0 billion
Schedule of Equity Method Investments [Line Items]
Management fee as percent of equity							1.50%
Fee percent of SAFE Equity over $5.0 billion | Minimum
Schedule of Equity Method Investments [Line Items]
Management fee equity threshold amount		$ 5,000,000,000.0					$ 5,000,000,000.0
SAFE
Schedule of Equity Method Investments [Line Items]
Equity interest (percent)		65.40%					65.40%
SAFE | Real estate equity investments
Schedule of Equity Method Investments [Line Items]
Voting power cap threshold (percent)	41.90%
Number of director nominees | director	3
Independent period	3 years
Standstill provisions (in years)	2 years
Exchange shares restriction period	1 year
Stock transfer limitation maximum per agreement, other than widely distributed public offering (percent)	20.00%
Ground Lease, Atlanta medical office
Schedule of Equity Method Investments [Line Items]
Commitment to provide loan to lessee										$ 24,000,000.0
Amount of loan funded										$ 18,400,000
Interest income								500,000
Multifamily Development San Jose
Schedule of Equity Method Investments [Line Items]
Amount of loan funded		$ 48,100,000					$ 48,100,000
Interest income							700,000	100,000
Lessor, operating lease, term of contract						99 years
Real estate, leasehold improvement allowance						$ 7,200,000
Forward purchase contract, purchase agreement, amount						34,000,000.0
Ground Lease, Multi-tenant Office Atlanta
Schedule of Equity Method Investments [Line Items]
Commitment to provide loan to lessee					$ 19,900,000
Interest income								600,000
Number of office buildings | office_building					2
Ground Lease, Washington DC building conversion
Schedule of Equity Method Investments [Line Items]
Commitment to provide loan to lessee				$ 13,300,000
Amount of loan funded		$ 12,800,000					12,800,000
Interest income							300,000	200,000
Leasehold First Mortgage | Multifamily Development San Jose
Schedule of Equity Method Investments [Line Items]
Commitment to provide loan to lessee						80,500,000
Carrying value of loans						$ 80,500,000
SAFE
Schedule of Equity Method Investments [Line Items]
Expense reimbursements from related party							1,300,000	500,000
SAFE | Management Fees
Schedule of Equity Method Investments [Line Items]
Management fee revenue from related party							$ 2,900,000	$ 1,500,000
SAFE
Schedule of Equity Method Investments [Line Items]
Ground lease term (in years)			98 years
Private Placement | SAFE
Schedule of Equity Method Investments [Line Items]
Shares acquired (in shares) | shares		1.7
Value of common stock issued in private placement		$ 80,000,000.0