Long-Term Debt - Maturities of Long-Term Debt (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Aug. 31, 2002	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2012
Debt Instrument [Line Items]
Less than one year		$ 71,640
One to two years		71,937
Two to three years		237,246
Three to four years		42,572
Four to five years		96,486
Over five years		256,410
Total debt		776,291
Less current maturities		(71,640)	$ (28,144)
Long-term debt, less current maturities		704,651
Unamortized debt discount		(14,963)
Long-term debt		689,688	523,228
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		195,000
Three to four years		0
Four to five years		0
Over five years		0
Total debt		255,000	277,500
Less current maturities		(30,000)
Long-term debt, less current maturities		225,000
Unamortized debt discount		0
Long-term debt		225,000
Convertible Senior Notes 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		200,000
Total debt		200,000	200,000	$ 200,000
Less current maturities		0
Long-term debt, less current maturities		200,000
Unamortized debt discount		(14,963)	(20,920)	$ (35,400)
Long-term debt		$ 185,037
Maturity date		March 2032
MARAD Debt 2027 [Member]
Debt Instrument [Line Items]
Less than one year		$ 5,926
One to two years		6,222
Two to three years		6,532
Three to four years		6,858
Four to five years		7,200
Over five years		56,410
Total debt		89,148	94,792
Less current maturities		(5,926)
Long-term debt, less current maturities		83,222
Unamortized debt discount		0
Long-term debt		83,222
Maturity date	February 2027
Nordea Q5000 Loan 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		89,286
Over five years		0
Total debt		232,143	$ 0
Less current maturities		(35,714)
Long-term debt, less current maturities		196,429
Unamortized debt discount		0
Long-term debt		$ 196,429