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Long-Term Debt - Schedule Of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Mar. 20, 2018	Dec. 31, 2017	Jun. 30, 2017	Nov. 01, 2016	Mar. 31, 2012
Debt Instrument [Line Items]
Principal amount	$ 479,161
Unamortized debt discounts	(28,802)		$ (14,406)
Unamortized debt issuance costs	(10,044)		(10,296)
Total debt	440,315		495,627
Less current maturities	(47,252)		(109,861)
Long-term debt	393,063		385,766
Term Loan Maturing June 2020
Debt Instrument [Line Items]
Principal amount	33,693		97,500	$ 100,000
Unamortized debt discounts	0
Unamortized debt issuance costs	(372)
Total debt	33,321
Less current maturities	(4,680)
Long-term debt	28,641
Convertible Senior Notes Maturing May 2022
Debt Instrument [Line Items]
Principal amount	125,000		125,000		$ 125,000
Unamortized debt discounts	(11,043)		(13,900)		$ (16,900)
Unamortized debt issuance costs	(1,765)
Total debt	112,192
Less current maturities	0
Long-term debt	112,192
Convertible Senior Notes Maturing September 2023
Debt Instrument [Line Items]
Principal amount	125,000	$ 125,000	0
Unamortized debt discounts	(17,759)	$ (20,100)
Unamortized debt issuance costs	(2,862)
Total debt	104,379
Less current maturities	0
Long-term debt	104,379
Convertible Senior Notes Maturing March 2032
Debt Instrument [Line Items]
Principal amount	0		60,115			$ 200,000
MARAD Debt Maturing February 2027
Debt Instrument [Line Items]
Principal amount	70,468		77,000
Unamortized debt discounts	0
Unamortized debt issuance costs	(4,025)
Total debt	66,443
Less current maturities	(6,858)
Long-term debt	59,585
Nordea Q5000 Loan Maturing April 2020
Debt Instrument [Line Items]
Principal amount	125,000		$ 160,714
Unamortized debt discounts	0
Unamortized debt issuance costs	(1,020)
Total debt	123,980
Less current maturities	(35,714)
Long-term debt	$ 88,266