Fair Value Measurements - Principal Amount And Estimated Fair Value Of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Aug. 14, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	$ 414,535
Term Loan Maturing December 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	30,625		$ 33,250
Fair value	30,051		32,959
Nordea Q5000 Loan Maturing January 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	62,500		89,286
Fair value	62,656		89,398
MARAD Debt Maturing February 2027
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	56,410		63,610
Fair value	62,551		68,643
Convertible Senior Notes Maturing May 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	35,000		125,000
Fair value	33,075		134,225
Convertible Senior Notes Maturing September 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	30,000		125,000
Fair value	27,300		162,188
Convertible Senior Notes Maturing February 2026
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	200,000	$ 200,000	0
Fair value	160,626		0
Total Debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	414,535		436,146
Fair value	$ 376,259		$ 487,413