Equity Investments - Narrative (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($) ft	Dec. 31, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Investee losses in excess of investment	$ 5,466	$ 6,035
Independence Hub, LLC
Schedule of Equity Method Investments [Line Items]
Percentage of ownership interest	20.00%
Water depth | ft	8,000
Investee losses in excess of investment	$ 10,600	$ 11,200