Investments - Summary of Amortization and Accretion Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Amortization of In-Place Leases, Amortization and Accretion of Above- and Below-Market Lease Assets and Liabilities [Line Items]
Amortization of in-place leases	$ 2,117	$ 1,253	$ 5,260	$ 3,698
Market Lease Intangibles | Rental Revenue
Amortization of In-Place Leases, Amortization and Accretion of Above- and Below-Market Lease Assets and Liabilities [Line Items]
Amortization (accretion) of market lease intangibles, net	245	727	642	1,161
Above and Below Market Ground Lease Intangibles | Property Expenses
Amortization of In-Place Leases, Amortization and Accretion of Above- and Below-Market Lease Assets and Liabilities [Line Items]
Amortization (accretion) of above- and below-market ground lease intangibles, net	$ (90)	$ (144)	$ (358)	$ (434)