Long-Term Debt - Maturities Of Long-Term Debt (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Aug. 31, 2002	Mar. 31, 2017	Dec. 31, 2016	Nov. 01, 2016	Mar. 31, 2012
Debt Instrument [Line Items]
Less than one year		$ 67,724
One to two years		202,622
Two to three years		42,741
Three to four years		87,735
Four to five years		7,746
Over five years		230,045
Total debt		638,613
Current maturities		(67,724)	$ (67,571)
Long-term debt, less current maturities		570,889
Unamortized debt discount		(17,950)
Unamortized debt issuance costs		(11,275)
Long-term debt		541,664	558,396
Term Loan Maturing June 2018 [Member]
Debt Instrument [Line Items]
Less than one year		25,634
One to two years		160,215
Two to three years		0
Three to four years		0
Four to five years		0
Over five years		0
Total debt		185,849	192,258
Current maturities		(25,634)
Long-term debt, less current maturities		160,215
Unamortized debt discount		0
Unamortized debt issuance costs		(1,159)
Long-term debt		159,056
Convertible Senior Notes Maturing May 2022 [Member]
Debt Instrument [Line Items]
Less than one year		0
One to two years		0
Two to three years		0
Three to four years		0
Four to five years		0
Over five years		125,000
Total debt		125,000	125,000	$ 125,000
Current maturities		0
Long-term debt, less current maturities		125,000
Unamortized debt discount		(15,873)	(16,500)	$ (16,900)
Unamortized debt issuance costs		(2,694)
Long-term debt		106,433
Convertible Senior Notes Maturing March 2032 [Member]
Debt Instrument [Line Items]
Less than one year		0
One to two years		0
Two to three years		0
Three to four years		0
Four to five years		0
Over five years		60,115
Total debt		60,115	60,115		$ 200,000
Current maturities		0
Long-term debt, less current maturities		60,115
Unamortized debt discount		(2,077)	(2,600)		$ (35,400)
Unamortized debt issuance costs		(185)
Long-term debt		$ 57,853
Maturity date		March 2032
MARAD Debt Maturing February 2027 [Member]
Debt Instrument [Line Items]
Less than one year		$ 6,375
One to two years		6,693
Two to three years		7,027
Three to four years		7,378
Four to five years		7,746
Over five years		44,930
Total debt		80,149	83,222
Current maturities		(6,375)
Long-term debt, less current maturities		73,774
Unamortized debt discount		0
Unamortized debt issuance costs		(4,879)
Long-term debt		68,895
Maturity date	February 2027
Nordea Q5000 Loan Maturing April 2020 [Member]
Debt Instrument [Line Items]
Less than one year		35,715
One to two years		35,714
Two to three years		35,714
Three to four years		80,357
Four to five years		0
Over five years		0
Total debt		187,500	$ 196,429
Current maturities		(35,715)
Long-term debt, less current maturities		151,785
Unamortized debt discount		0
Unamortized debt issuance costs		(2,358)
Long-term debt		$ 149,427