Fair Value Measurements - Carrying Values and Estimated Fair Values of Long-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015	Mar. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 733,256
Term Loan Maturing June 2018 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	240,000	$ 255,000
Fair Value	237,300	248,467
Nordea Q5000 Loan Maturing April 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	214,285	232,143
Fair Value	207,724	221,553
MARAD Debt Maturing February 2027 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	86,221	89,148
Fair Value	98,233	104,897
Convertible Senior Notes Maturing March 2032 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	192,750	200,000	$ 200,000
Fair Value	169,620	150,250
Loan Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	733,256	776,291
Fair Value	$ 712,877	$ 725,167