Investments - Summary of Amortization and Accretion Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 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	$ 1,914	$ 1,197	$ 3,143	$ 2,445
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	118	224	398	434
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	$ (127)	$ (89)	$ (268)	$ (290)