Fair Value Measurements and Derivative Instruments - Equity Method Investments (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt facility and other receivables due from Skysea Holding		$ 277,635	$ 314,323
Fair Value, Measurements, Nonrecurring | Total Carrying Amount
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity-method investment- SkySea Holding	[1]	0
Debt facility and other receivables due from Skysea Holding	[2]	64,667
Total		64,667
Fair Value, Measurements, Nonrecurring | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity-method investment- SkySea Holding	[1]	0
Debt facility and other receivables due from Skysea Holding	[2]	64,667
Total		64,667
Fair Value, Measurements, Nonrecurring | Total Fair Value | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity-method investment- SkySea Holding	[1]	0
Debt facility and other receivables due from Skysea Holding	[2]	64,667
Total		64,667
Fair Value, Measurements, Nonrecurring | Total Impairment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Equity-method investment- SkySea Holding	[1]	509
Debt facility and other receivables due from Skysea Holding	[2]	22,834
Total		$ 23,343

[1] Due to the expectation that Skysea Holding will cease business operations by the end of 2018, we do not deem our investment balance to be recoverable and therefore, we estimated the fair value of our investment to be zero. The fair value of our equity investment in Skysea Holding was estimated as of March 31, 2018, the date of the last impairment test, at which point the investment was fully impaired.

[2] We estimated the fair value of our debt facility and other receivables due from Skysea Holding based on the fair value of the collateral of the debt facility, Skysea Holding's ship, Golden Era, as of March 31, 2018, the date of the last impairment test, adjusted for foreign exchange rates as of June 30, 2018. We believe this amount estimates fair value as of June 30, 2018. The fair value of the ship represents the net realizable value based on the agreed upon sale price of the ship, which is expected to be completed in December 2018. For further information on the Skysea Holding impairment, refer to Note 5. Other Assets.