Fair Value Measurements - Carrying Values and Estimated Fair Values of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Mar. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	$ 698,195
Term Loan Maturing June 2018 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	224,500	$ 255,000
Fair Value	223,658	248,467
Nordea Q5000 Loan Maturing April 2020 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	205,357	232,143
Fair Value	201,123	221,553
MARAD Debt Maturing February 2027 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	83,222	89,148
Fair Value	95,015	104,897
Convertible Senior Notes Maturing March 2032 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	185,116	200,000	$ 200,000
Fair Value	177,711	150,250
Loan Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value	698,195	776,291
Fair Value	$ 697,507	$ 725,167