Fair Value Measurements - Principal Amount And Estimated Fair Value Of Long-Term Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	$ 309,930	$ 313,850
Fair value	338,219	316,891
MARAD Debt Maturing February 2027
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	44,930	48,850
Fair value	46,688	52,481
Convertible Senior Notes Maturing May 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	35,000	35,000
Fair value	35,022	34,794
Convertible Senior Notes Maturing September 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Principal amount	30,000	30,000
Fair value	29,693	29,054
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
Fair value	$ 226,816	$ 200,562