Equity Investments in Real Estate - Ownership Interest in Equity Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Ownership interest in equity investments:
Equity investments in real estate	$ 397,896	$ 409,254
Net Lease
Ownership interest in equity investments:
Equity investments in real estate	$ 358,218	370,530
Net Lease | Third Party | Kesko Senukai
Ownership interest in equity investments:
Ownership interest (as a percentage)	70.00%
Equity investments in real estate	$ 55,769	58,136
Net Lease | Third Party | BPS Nevada, LLC
Ownership interest in equity investments:
Ownership interest (as a percentage)	15.00%
Equity investments in real estate	$ 23,435	23,455
Net Lease | WPC | Hellweg Die Profi-Baumärkte GmbH & Co. KG (referred to as Hellweg 2)
Ownership interest in equity investments:
Ownership interest (as a percentage)	37.00%
Equity investments in real estate	$ 107,125	109,933
Net Lease | WPC | Jumbo Logistiek Vastgooed B.V
Ownership interest in equity investments:
Ownership interest (as a percentage)	85.00%
Equity investments in real estate	$ 52,090	55,162
Net Lease | WPC | U-Haul Moving Partners, Inc. and Mercury Partners, LP
Ownership interest in equity investments:
Ownership interest (as a percentage)	12.00%
Equity investments in real estate	$ 35,053	35,897
Net Lease | WPC | Berry Global Inc.
Ownership interest in equity investments:
Ownership interest (as a percentage)	50.00%
Equity investments in real estate	$ 14,045	14,476
Net Lease | WPC | Tesco Global Aruhazak Zrt.
Ownership interest in equity investments:
Ownership interest (as a percentage)	49.00%
Equity investments in real estate	$ 10,266	10,707
Net Lease | WPC | Eroski Sociedad Cooperativa - Mallorca
Ownership interest in equity investments:
Ownership interest (as a percentage)	30.00%
Equity investments in real estate	$ 7,352	7,629
Net Lease | WPC | Dick’s Sporting Goods, Inc.
Ownership interest in equity investments:
Ownership interest (as a percentage)	45.00%
Equity investments in real estate	$ 3,396	3,750
Net Lease | CPA 18 - Global | Bank Pekao S.A.
Ownership interest in equity investments:
Ownership interest (as a percentage)	50.00%
Equity investments in real estate	$ 23,945	25,582
Net Lease | CPA 18 - Global | State Farm
Ownership interest in equity investments:
Ownership interest (as a percentage)	50.00%
Equity investments in real estate	$ 15,261	16,072
Net Lease | CPA 18 - Global | Apply Sorco AS
Ownership interest in equity investments:
Ownership interest (as a percentage)	49.00%
Equity investments in real estate	$ 7,328	6,298
Net Lease | CPA 18 - Global | Konzum d.d. (referred to as Agrokor)
Ownership interest in equity investments:
Ownership interest (as a percentage)	20.00%
Equity investments in real estate	$ 3,153	3,433
All Other
Ownership interest in equity investments:
Equity investments in real estate	$ 39,678	38,724
All Other | Third Party | BG LLH, LLC
Ownership interest in equity investments:
Ownership interest (as a percentage)	6.00%
Equity investments in real estate	$ 39,678	$ 38,724