Investments - Summary of Gross Investment Activity (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2020 USD ($) InvestmentLocation	Jun. 30, 2019 USD ($) InvestmentLocation	Dec. 31, 2019 USD ($)
Number of Investment Locations
Beginning balance | InvestmentLocation	1,000	677
Acquisitions of and additions to real estate investments | InvestmentLocation	73	137
Sales of investments in real estate | InvestmentLocation	(13)	(18)
Relinquishment of properties at end of ground lease term | InvestmentLocation	(3)	(1)
Investments in loans receivable | InvestmentLocation	3	5
Principal collections on direct financing lease receivables | InvestmentLocation		(11)
Ending balance | InvestmentLocation	1,060	789
Real Estate Investment Property, at Cost [Roll Forward]
Beginning balance	$ 2,002,314	$ 1,394,549
Acquisitions of and additions to real estate investments	207,774	290,943
Sales of investments in real estate	(21,882)	(35,383)
Relinquishment of properties at end of ground lease term	(1,931)	(241)
Provisions for impairment of real estate	(1,859)	(1,921)
Investments in loans receivable	9,656	23,566
Principal collections on direct financing lease receivables	(130)	(10,412)
Other	(1,328)	(866)
Ending balance	2,192,614	1,660,235
Less: accumulated depreciation and amortization	(113,235)	(69,010)	$ (90,071)
Net investments	$ 2,079,379	$ 1,591,225	$ 1,912,243