Equity Investments in Real Estate - Ownership Interest in Equity Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2017	May 23, 2017	Dec. 31, 2016	Dec. 31, 2012
Ownership interest in equity investments:
Equity investments in real estate	$ 409,254		$ 451,105
Shelborne Property Associates, LLC
Ownership interest in equity investments:
Ownership interest, percentage				33.00%
Net Lease
Ownership interest in equity investments:
Equity investments in real estate	$ 370,530		222,342
Net Lease | Third Party | Kesko Senukai
Ownership interest in equity investments:
Ownership interest, percentage	70.00%	70.00%
Equity investments in real estate	$ 58,136		0
Net Lease | Third Party | BPS Nevada, LLC
Ownership interest in equity investments:
Ownership interest, percentage	15.00%
Equity investments in real estate	$ 23,455		23,036
Net Lease | WPC | Hellweg Die Profi-Baumärkte GmbH & Co. KG (referred to as Hellweg 2)
Ownership interest in equity investments:
Ownership interest, percentage	37.00%
Equity investments in real estate	$ 109,933		10,125
Net Lease | WPC | Jumbo Logistiek Vastgooed B.V
Ownership interest in equity investments:
Ownership interest, percentage	85.00%
Equity investments in real estate	$ 55,162		54,621
Net Lease | WPC | U-Haul Moving Partners, Inc. and Mercury Partners, LP (b)
Ownership interest in equity investments:
Ownership interest, percentage	12.00%
Equity investments in real estate	$ 35,897		37,601
Net Lease | WPC | Berry Global Inc.
Ownership interest in equity investments:
Ownership interest, percentage	50.00%
Equity investments in real estate	$ 14,476		14,974
Net Lease | WPC | Tesco Global Aruhazak Zrt.
Ownership interest in equity investments:
Ownership interest, percentage	49.00%
Equity investments in real estate	$ 10,707		10,807
Net Lease | WPC | Eroski Sociedad Cooperativa - Mallorca
Ownership interest in equity investments:
Ownership interest, percentage	30.00%
Equity investments in real estate	$ 7,629		6,576
Net Lease | WPC | Dick’s Sporting Goods, Inc.
Ownership interest in equity investments:
Ownership interest, percentage	45.00%
Equity investments in real estate	$ 3,750		4,367
Net Lease | CPA 18 - Global | Bank Pekao S.A.
Ownership interest in equity investments:
Ownership interest, percentage	50.00%
Equity investments in real estate	$ 25,582		23,025
Net Lease | CPA 18 - Global | State Farm Automobile Co.
Ownership interest in equity investments:
Ownership interest, percentage	50.00%
Equity investments in real estate	$ 16,072		17,603
Net Lease | CPA 18 - Global | Apply Sorco AS
Ownership interest in equity investments:
Ownership interest, percentage	49.00%
Equity investments in real estate	$ 6,298		12,528
Net Lease | CPA 18 - Global | Konzum d.d. (referred to as Agrokor)
Ownership interest in equity investments:
Ownership interest, percentage	20.00%
Equity investments in real estate	$ 3,433		7,079
All Other
Ownership interest in equity investments:
Equity investments in real estate	$ 38,724		228,763
All Other | Third Party | BG LLH, LLC
Ownership interest in equity investments:
Ownership interest, percentage	6.00%
Equity investments in real estate	$ 38,724		36,756
All Other | Third Party | Shelborne Property Associates, LLC
Ownership interest in equity investments:
Ownership interest, percentage				33.00%
Equity investments in real estate	0		127,424
All Other | Third Party | IDL Wheel Tenant, LLC
Ownership interest in equity investments:
Equity investments in real estate	0		37,124
All Other | Third Party | BPS Nevada, LLC Preferred Equity
Ownership interest in equity investments:
Equity investments in real estate	$ 0		$ 27,459