Long-Term Debt - Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Aug. 31, 2002	Jun. 30, 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		222,407
Three to four years		114,169
Four to five years		7,378
Over five years		245,426
Total debt		733,256
Current maturities		(71,786)	$ (71,640)
Long-term debt, less current maturities		661,470
Unamortized debt discount		(11,400)
Unamortized debt issuance costs		(11,085)
Long-term debt		638,985	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		180,000
Total debt		240,000	255,000
Current maturities		(30,000)
Long-term debt, less current maturities		210,000
Unamortized debt issuance costs		(1,855)
Long-term debt		208,145
Convertible Senior Notes Maturing March 2032 [Member]
Debt Instrument [Line Items]
Over five years		192,750
Total debt		192,750	200,000	$ 200,000
Long-term debt, less current maturities		192,750
Unamortized debt discount		(11,400)	(15,000)	$ (35,400)
Unamortized debt issuance costs		(1,036)
Long-term debt		$ 180,314
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		(5,245)
Long-term debt		74,904
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		107,142
Total debt		214,285	$ 232,143
Current maturities		(35,714)
Long-term debt, less current maturities		178,571
Unamortized debt issuance costs		(2,949)
Long-term debt		$ 175,622