Long-Term Debt - Maturities Of Long-Term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jun. 28, 2019	Dec. 31, 2018	Mar. 20, 2018	Nov. 01, 2016
Debt Instrument [Line Items]
Less than one year	$ 99,986
One to two years	37,310
Two to three years	132,937
Three to four years	133,333
Four to five years	8,749
Over five years	23,831
Gross debt	436,146
Unamortized debt discounts	(22,540)		$ (28,802)
Unamortized debt issuance costs	(7,753)		(10,044)
Total debt	405,853		440,315
Less current maturities	(99,731)		(47,252)
Long-term debt	306,122		393,063
Term Loan Maturing December 2021
Debt Instrument [Line Items]
Less than one year	3,500
One to two years	29,750
Two to three years	0
Three to four years	0
Four to five years	0
Over five years	0
Gross debt	33,250	$ 35,000	0
Unamortized debt discounts	0
Unamortized debt issuance costs	(381)
Total debt	32,869
Less current maturities	(3,500)
Long-term debt	29,369
Convertible Senior Notes Maturing May 2022
Debt Instrument [Line Items]
Less than one year	0
One to two years	0
Two to three years	125,000
Three to four years	0
Four to five years	0
Over five years	0
Gross debt	125,000		125,000		$ 125,000
Unamortized debt discounts	(7,999)		(11,000)		$ (16,900)
Unamortized debt issuance costs	(1,236)
Total debt	115,765
Less current maturities	0
Long-term debt	115,765
Convertible Senior Notes Maturing September 2023
Debt Instrument [Line Items]
Less than one year	0
One to two years	0
Two to three years	0
Three to four years	125,000
Four to five years	0
Over five years	0
Gross debt	125,000		125,000	$ 125,000
Unamortized debt discounts	(14,541)		(17,800)	$ (20,100)
Unamortized debt issuance costs	(2,344)
Total debt	108,115
Less current maturities	0
Long-term debt	108,115
MARAD Debt Maturing February 2027
Debt Instrument [Line Items]
Less than one year	7,200
One to two years	7,560
Two to three years	7,937
Three to four years	8,333
Four to five years	8,749
Over five years	23,831
Gross debt	63,610		70,468
Unamortized debt discounts	0
Unamortized debt issuance costs	(3,537)
Total debt	60,073
Less current maturities	(7,200)
Long-term debt	52,873
Nordea Q5000 Loan Maturing April 2020
Debt Instrument [Line Items]
Less than one year	89,286
One to two years	0
Two to three years	0
Three to four years	0
Four to five years	0
Over five years	0
Gross debt	89,286		$ 125,000
Unamortized debt discounts	0
Unamortized debt issuance costs	(255)
Total debt	89,031
Less current maturities	(89,031)
Long-term debt	$ 0