Commitments and Contingencies - Purchase Commitments Narrative (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) property agreement	Dec. 31, 2017 USD ($)
Unrecorded Unconditional Purchase Obligation [Line Items]
Escrow deposits	$ 4,573	$ 4,995
Purchase Commitment [Member]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of purchase and sale agreements | agreement	13
Percentage of voting interests acquired	100.00%
Number of properties acquired | property	13
Aggregate purchase price	$ 244,500
Escrow deposits	$ 4,600