Investments - Additional Information (Details) $ in Thousands		3 Months Ended
	Apr. 01, 2019 USD ($) Property	Mar. 31, 2019 USD ($) Loan Property Investment	Mar. 31, 2018 USD ($) Loan Investment	Dec. 31, 2018 USD ($) Loan Property Investment	Dec. 31, 2017 USD ($)
Investment [Line Items]
Number of property locations of investments | Property		708		665
Number of property development in progress | Property		6		4
Number of real estate properties undeveloped land parcels | Property		1		1
Number of mortgage loans receivable | Loan		2		3
Number of additional properties secured for mortgage loan receivable | Property		3		12
Number of owned properties | Property		696		652
Number of properties owned as direct financing receivables | Property		5		5
Number of ground lease interests | Property		12		13
Number of real estate subject to direct financing leases | Property		1		1
Gross acquisition cost of real estate investments		$ 1,500,050	$ 994,140	$ 1,394,549	$ 939,072
Real estate investments, at cost		1,484,342		1,377,044
Aggregate carrying amount of loans and direct financing lease receivable		11,900		$ 17,500
Real estate investments held for sale, net		$ 3,800
Number of investments | Investment		349		347
Net investments		$ 611,900		$ 609,200
Number of acquisitions represented more than five percentage of total investment activity | Investment		0	0
Number of loan receivable agreements secured | Loan		3	0	4
Aggregate carrying value of loans receivable		$ 9,300		$ 14,900
Proceeds from loans receivable		5,700
Aggregate carrying amount of direct financing lease receivable		$ 2,600		$ 2,600
Subsequent Event
Investment [Line Items]
Number of real estate investment properties acquired | Property	9
Aggregate investment (including acquisition-related costs)	$ 14,600
Investment in new and ongoing construction in progress	$ 1,100
Number of investment properties sold or transferred | Property	5
Investment, aggregate gross sales price	$ 11,100
Investment, disposition costs	$ 500