Equity Investments in the Managed Programs and Real Estate - Narratives (Details) - USD ($)	1 Months Ended	3 Months Ended
	Jan. 31, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Investments in REITs
Distributions of earnings from equity method investments		$ 15,289,000	$ 16,848,000
Payments to acquire equity method investments		715,000	0
Owned Real Estate | Unconsolidated Real Estate Investment
Investments in REITs
Distributions of earnings from equity method investments		$ 4,400,000	3,800,000
Owned Real Estate | The New York Times Company
Investments in REITs
Payments to acquire equity method investments	$ 112,500,000
CPA: 17 - Global
Investments in REITs
Asset management fees receivable, shares		248,746
Distributions of earnings from equity method investments		$ 2,400,000	1,900,000
CPA: 17 - Global | Owned Real Estate | The New York Times Company
Investments in REITs
Payments to acquire equity method investments	250,000,000
CPA: 17 - Global | Owned Real Estate | Jumbo Logestiek Vastgoed B.V.
Investments in REITs
Mortgage debt tenants in common		77,900,000
Pro rata share mortgage debt on tenancy in common		11,700,000
CPA: 17 - Global | Owned Real Estate | Wanbishi Archives Co. Ltd.
Investments in REITs
Contributions to equity method investments	$ 700,000
CPA:17 - Global operating partnership
Investments in REITs
Distributions of earnings from equity method investments		6,200,000	6,800,000
CPA:18 - Global
Investments in REITs
Distributions of earnings from equity method investments		$ 600,000	300,000
CPA:18 - Global | Class A
Investments in REITs
Asset management fees receivable, shares		114,835
CPA:18 - Global operating partnership
Investments in REITs
Distributions of earnings from equity method investments		$ 1,900,000	1,700,000
CWI
Investments in REITs
Asset management fees receivable, shares		114,027
Distributions of earnings from equity method investments		$ 400,000	200,000
CWI operating partnership
Investments in REITs
Distributions of earnings from equity method investments		1,000,000	1,700,000
CWI 2
Investments in REITs
Distributions of earnings from equity method investments		$ 200,000	100,000
CWI 2 | Class A
Investments in REITs
Asset management fees receivable, shares		83,586
CWI 2 operating partnership
Investments in REITs
Distributions of earnings from equity method investments		$ 1,500,000	1,600,000
CESH I
Investments in REITs
Distributions of earnings from equity method investments		0	0
CCIF
Investments in REITs
Distributions of earnings from equity method investments			$ 300,000
CCIF | Other assets, net
Investments in REITs
Cost method equity investments		23,200,000		$ 23,300,000
Managed Programs
Investments in REITs
Aggregate unamortized basis difference on equity investments		$ 45,400,000		$ 42,500,000