Noncontrolling Interest of Unitholders in Operating Partnership - Additional Information (Details) $ / shares in Units, $ in Thousands			3 Months Ended
	Mar. 31, 2018 USD ($) shares	Mar. 31, 2017 USD ($)	Mar. 31, 2018 item $ / shares shares	Mar. 31, 2017 $ / shares	Dec. 31, 2017 shares
Noncontrolling Interest
Distributions per unit | $ / shares			$ 0.254375	$ 0.2475
Maximum
Noncontrolling Interest
Number of permitted exchange requests in a calendar year | item			2
Limited Partnership
Noncontrolling Interest
Total units	17,582,000		17,582,000		17,517,000
Limited Partnership | Minimum
Noncontrolling Interest
Number of units which can be redeemed in single redemption			1,000
Operating Partnership
Noncontrolling Interest
Declared distributions | $	$ 4,473	$ 4,232