Long-Term Debt - Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended
	Aug. 31, 2002	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2012
Debt Instrument [Line Items]
Less than one year		$ 71,786
One to two years		72,090
Two to three years		229,907
Three to four years		42,741
Four to five years		87,735
Over five years		252,676
Total debt		756,935
Current maturities		(71,786)	$ (71,640)
Long-term debt, less current maturities		685,149
Unamortized debt discount		(13,396)
Unamortized debt issuance costs		(11,805)
Long-term debt		659,948	677,695
Term Loan Maturing June 2018 [Member]
Debt Instrument [Line Items]
Less than one year		30,000
One to two years		30,000
Two to three years		187,500
Total debt		247,500	255,000
Current maturities		(30,000)
Long-term debt, less current maturities		217,500
Unamortized debt issuance costs		(2,087)
Long-term debt		215,413
Convertible Senior Notes Maturing March 2032 [Member]
Debt Instrument [Line Items]
Over five years		200,000
Total debt		200,000	200,000	$ 200,000
Long-term debt, less current maturities		200,000
Unamortized debt discount		(13,396)	(15,000)	$ (35,400)
Unamortized debt issuance costs		(1,229)
Long-term debt		$ 185,375
Maturity date		March 2032
MARAD Debt Maturing February 2027 [Member]
Debt Instrument [Line Items]
Less than one year		$ 6,072
One to two years		6,375
Two to three years		6,693
Three to four years		7,027
Four to five years		7,378
Over five years		52,676
Total debt		86,221	89,148
Current maturities		(6,072)
Long-term debt, less current maturities		80,149
Unamortized debt issuance costs		(5,367)
Long-term debt		74,782
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		35,715
Two to three years		35,714
Three to four years		35,714
Four to five years		80,357
Total debt		223,214	$ 232,143
Current maturities		(35,714)
Long-term debt, less current maturities		187,500
Unamortized debt issuance costs		(3,122)
Long-term debt		$ 184,378