Long-Term Debt - Maturities Of Long-Term Debt (Details) - USD ($) $ in Thousands		1 Months Ended	9 Months Ended
	Jun. 30, 2017	Aug. 31, 2002	Sep. 30, 2017	Dec. 31, 2016	Nov. 01, 2016	Mar. 31, 2012
Debt Instrument [Line Items]
Less than one year			$ 108,611
One to two years			53,822
Two to three years			186,665
Three to four years			7,560
Four to five years			132,937
Over five years			40,913
Total debt			530,508
Current maturities			(108,611)	$ (67,571)
Long-term debt, less current maturities			421,897
Unamortized debt discount			(15,607)
Unamortized debt issuance costs			(10,945)
Long-term debt			395,345	558,396
Term Loan Maturing June 2020 [Member]
Debt Instrument [Line Items]
Less than one year			6,250
One to two years			11,250
Two to three years			81,250
Three to four years			0
Four to five years			0
Over five years			0
Total debt	$ 100,000		98,750	0
Current maturities			(6,250)
Long-term debt, less current maturities			92,500
Unamortized debt discount			0
Unamortized debt issuance costs			(1,815)
Long-term debt			90,685
Maturity date	June 2020
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			125,000
Over five years			0
Total debt			125,000	125,000	$ 125,000
Current maturities			0
Long-term debt, less current maturities			125,000
Unamortized debt discount			(14,555)	(16,500)	$ (16,900)
Unamortized debt issuance costs			(2,427)
Long-term debt			$ 108,018
Maturity date			May 2022
Convertible Senior Notes Maturing March 2032 [Member]
Debt Instrument [Line Items]
Less than one year			$ 60,115
One to two years			0
Two to three years			0
Three to four years			0
Four to five years			0
Over five years			0
Total debt			60,115	60,115		$ 200,000
Current maturities			(60,115)
Long-term debt, less current maturities			0
Unamortized debt discount			(1,052)	(2,600)		$ (35,400)
Unamortized debt issuance costs			(92)
Long-term debt			$ (1,144)
Earliest put date			March 2018
MARAD Debt Maturing February 2027 [Member]
Debt Instrument [Line Items]
Less than one year			$ 6,532
One to two years			6,858
Two to three years			7,200
Three to four years			7,560
Four to five years			7,937
Over five years			40,913
Total debt			77,000	83,222
Current maturities			(6,532)
Long-term debt, less current maturities			70,468
Unamortized debt discount			0
Unamortized debt issuance costs			(4,635)
Long-term debt			65,833
Maturity date		February 2027
Nordea Q5000 Loan Maturing April 2020 [Member]
Debt Instrument [Line Items]
Less than one year			35,714
One to two years			35,714
Two to three years			98,215
Three to four years			0
Four to five years			0
Over five years			0
Total debt			169,643	$ 196,429
Current maturities			(35,714)
Long-term debt, less current maturities			133,929
Unamortized debt discount			0
Unamortized debt issuance costs			(1,976)
Long-term debt			$ 131,953