Long-Term Debt - Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	Aug. 31, 2002	Sep. 30, 2016	Dec. 31, 2015	Mar. 31, 2012
Debt Instrument [Line Items]
Less than one year		$ 70,905
One to two years		237,778
Two to three years		42,572
Three to four years		105,414
Four to five years		7,560
Over five years		233,966
Total debt		698,195
Current maturities		(70,905)	$ (71,640)
Long-term debt, less current maturities		627,290
Unamortized debt discount		(9,448)
Unamortized debt issuance costs		(10,340)
Long-term debt		607,502	677,695
Term Loan Maturing June 2018 [Member]
Debt Instrument [Line Items]
Less than one year		28,968
One to two years		195,532
Total debt		224,500	255,000
Current maturities		(28,968)
Long-term debt, less current maturities		195,532
Unamortized debt issuance costs		(1,623)
Long-term debt		193,909
Convertible Senior Notes Maturing March 2032 [Member]
Debt Instrument [Line Items]
Over five years		185,116
Total debt		185,116	200,000	$ 200,000
Long-term debt, less current maturities		185,116
Unamortized debt discount		(9,448)	(15,000)	$ (35,400)
Unamortized debt issuance costs		(853)
Long-term debt		$ 174,815
Maturity date		March 2032
MARAD Debt Maturing February 2027 [Member]
Debt Instrument [Line Items]
Less than one year		$ 6,222
One to two years		6,532
Two to three years		6,858
Three to four years		7,200
Four to five years		7,560
Over five years		48,850
Total debt		83,222	89,148
Current maturities		(6,222)
Long-term debt, less current maturities		77,000
Unamortized debt issuance costs		(5,123)
Long-term debt		71,877
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		98,214
Total debt		205,357	$ 232,143
Current maturities		(35,715)
Long-term debt, less current maturities		169,642
Unamortized debt issuance costs		(2,741)
Long-term debt		$ 166,901