Long-Term Debt - Maturities Of Long-Term Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Less than one year	$ 42,937
One to two years	38,333
Two to three years	8,749
Three to four years	9,186
Four to five years	209,644
Over five years	5,001
Gross debt	313,850	$ 404,732
Unamortized debt issuance costs	(9,357)
Total debt	304,493
Less: current maturities	(42,825)	(90,651)
Long-term debt	261,668	258,912
Convertible Senior Notes Maturing May 2022
Debt Instrument [Line Items]
Less than one year	35,000
Gross debt	35,000	35,000
Unamortized debt issuance costs	(112)
Total debt	34,888
Less: current maturities	(34,888)
Convertible Senior Notes Maturing September 2023
Debt Instrument [Line Items]
One to two years	30,000
Gross debt	30,000	30,000
Unamortized debt issuance costs	(359)
Total debt	29,641
Long-term debt	29,641
Convertible Senior Notes Maturing February 2026
Debt Instrument [Line Items]
Four to five years	200,000
Gross debt	200,000	200,000
Unamortized debt issuance costs	(6,203)
Total debt	193,797
Long-term debt	193,797
MARAD Debt Maturing February 2027
Debt Instrument [Line Items]
Less than one year	7,937
One to two years	8,333
Two to three years	8,749
Three to four years	9,186
Four to five years	9,644
Over five years	5,001
Gross debt	48,850	$ 56,410
Unamortized debt issuance costs	(2,683)
Total debt	46,167
Less: current maturities	(7,937)
Long-term debt	$ 38,230

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt issuance costs classified as noncurrent. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next rolling twelve months following the latest balance sheet. For interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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