Revenue Concentration (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) item	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Concentration Risk [Line Items]
Revenues	$ 94,034	$ 90,161	$ 82,692	$ 81,506	$ 77,274	$ 78,472	$ 71,642	$ 66,966	$ 348,393	$ 294,354	$ 249,667
Ten Largest Container Lessees [Member] | Customer Concentration Risk [Member] | Total Revenue [Member]
Concentration Risk [Line Items]
Number of major customers | item									10
Percentage of operations comprised by segment									44.50%	41.50%	51.90%
Single Largest Container Lessee [Member] | Customer Concentration Risk [Member] | Total Revenue [Member]
Concentration Risk [Line Items]
Percentage of operations comprised by segment									10.80%	10.80%	11.60%
Revenues									$ 37,500	$ 31,700	$ 29,000
Second Largest Container Lessee [Member] | Customer Concentration Risk [Member] | Total Revenue [Member]
Concentration Risk [Line Items]
Percentage of operations comprised by segment									10.00%	7.00%	8.40%
Revenues									$ 34,700	$ 20,600	$ 21,100