Real Estate - Narrative (Details) $ in Thousands, ft² in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) ft² state Property building	Mar. 31, 2017 USD ($)
Real Estate Properties [Line Items]
Number of properties (property) | Property	27
Number of buildings (building) | building	35
Number of states (state) | state	17
Aggregate purchase price of acquired properties	$ 1,100,000
Area of real estate property (in sqft) | ft²	7.3
Depreciation of building and improvements	$ 5,031	$ 4,892
Amortization expense	$ 6,000