Investment in Unconsolidated Entities - Cash Received and Distributions (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
NewINK Joint Venture
Schedule of Equity Method Investments [Line Items]
Cash generated from other activities and excess cash	$ 1,182	$ 1,182	$ 2,775	$ 1,901
Total	1,182	1,182	2,775	1,901
Inland Joint Venture
Schedule of Equity Method Investments [Line Items]
Cash generated from other activities and excess cash	200	100	1,450	100
Total	$ 200	$ 100	$ 1,450	$ 100

Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Includes effect from exchange rate changes.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration