Long-Term Debt (Narrative) (Details) (USD $)	3 Months Ended		9 Months Ended						1 Months Ended	3 Months Ended		1 Months Ended	9 Months Ended			1 Months Ended	3 Months Ended	1 Months Ended			3 Months Ended	9 Months Ended		1 Months Ended			3 Months Ended	9 Months Ended			1 Months Ended		3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2013		Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2013 Interest Rate Swaps [Member]	Sep. 30, 2013 Revolving Credit Facility Maturing June 2018 [Member]	Jul. 31, 2013 Term Loan Maturing June 2018 [Member]	Sep. 30, 2013 Term Loan Maturing June 2018 [Member]		Mar. 31, 2012 Convertible Senior Notes 2032 [Member]	Sep. 30, 2013 Convertible Senior Notes 2032 [Member]		Dec. 31, 2012 Convertible Senior Notes 2032 [Member]	Feb. 28, 2013 Helix Term Loan [Member]	Jun. 30, 2013 Helix Term Loan [Member]	Jun. 30, 2013 Revolving Credit Facility [Member]	Jul. 22, 2013 Senior Unsecured Notes [Member]	Mar. 31, 2012 Senior Unsecured Notes [Member]	Sep. 30, 2013 Senior Unsecured Notes [Member]	Sep. 30, 2012 Senior Unsecured Notes [Member]	Dec. 31, 2007 Senior Unsecured Notes [Member]	Feb. 28, 2013 Convertible Senior Notes 2025 [Member]	Dec. 31, 2012 Convertible Senior Notes 2025 [Member]	Mar. 31, 2005 Convertible Senior Notes 2025 [Member]	Mar. 31, 2012 Convertible Senior Notes 2025 [Member]	Sep. 30, 2012 Convertible Senior Notes 2025 [Member]	Sep. 30, 2013 MARAD Debt [Member]	Sep. 30, 2005 MARAD Debt [Member]	Jun. 30, 2013 Credit Agreement [Member]	Feb. 28, 2013 Credit Agreement [Member]	Sep. 30, 2013 Minimum [Member] London Interbank Offered Rate (LIBOR) [Member]	Sep. 30, 2013 Minimum [Member] Base Rate [Member]	Sep. 30, 2013 Maximum [Member] London Interbank Offered Rate (LIBOR) [Member]	Sep. 30, 2013 Maximum [Member] Base Rate [Member]	Sep. 30, 2013 Years three through five	Sep. 30, 2013 Years one and two
Debt Instrument [Line Items]
Original borrowing capacity								$ 600,000,000		$ 300,000,000
Notional Amount of Derivative							148,100,000
Debt Instrument, Periodic Payment, Principal, Percentage																																					10.00%	5.00%
Debt Instrument, Periodic Payment, Principal																																					30,000,000	15,000,000
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid										180,000,000
Debt instrument interest rate												3.25%											9.50%			3.25%				4.93%
Base Principal Amount															1,000
Issuance Of Notes Percentage													100.00%
Convertible Senior Notes, shares of common stock													39.9752
Senior Unsecured Notes amount issued																							550,000,000
Unsecured letters of credit	6,600,000		6,600,000
Long-term debt, less current maturities	548,204,000		548,204,000			1,002,621,000				281,250,000	[1]		172,162,000	[2]															94,792,000
Long-term debt, Carrying Value										296,250,000		200,000,000														300,000,000			100,168,000
Aggregate amount of debt payment			281,490,000		209,500,000														282,000,000	213,500,000
Repayments of debt																		70,300,000	275,000,000	200,000,000											80,100,000
Premium on debt extinguishment																			6,500,000	9,500,000							1,800,000
Accrued interest on notes																			500,000	4,000,000							1,100,000
Accelerated amortization of debt discount			3,850,000		7,253,000																							3,500,000
Loss on early extinguishment of debt	8,572,000		12,100,000		17,127,000																8,600,000	11,500,000						5,600,000
Line Of Credit Facility, Maximum Additional Commitments			200,000,000
Debt Instrument, Basis Spread on Variable Rate										2.50%																			0.20%				2.00%	1.00%	3.00%	2.00%
Revolving credit facility available	593,400,000		593,400,000
Debt instrument issued percentage																										100.00%
Effective interest rate													6.90%
Per share conversion price													$ 25.02
Amortization of deferred financing costs			4,091,000		4,990,000											2,900,000	600,000				2,100,000	2,000,000						300,000
Debt Instrument, Repurchase Amount																											142,200,000
Proceeds from Issuance of Debt												195,000,000
Debt percentage guaranteed																													50.00%
Debt Instrument, Unamortized Discount	27,838,000	[3]	27,838,000	[3]								35,400,000	27,838,000	[2],[3]
Expected life used to estimate fair value			6 years
Deferred financing costs			10,948,000		7,766,000
Repayments of debt			370,931,000		10,585,000																			3,500,000	154,300,000							318,400,000
Line of Credit Facility, Commitment Fee Percentage	0.50%
Repayments of Convertible Debt			3,487,000		143,945,000																						145,100,000
Proceeds from Issuance of Other Long-term Debt			$ 300,000,000		$ 100,000,000				$ 300,000,000

[1] Amount reflects the borrowings made in July 2013 (see “Credit Agreement” below).

[2] Beginning in March 2018, the holders of the Convertible Senior Notes due 2032 may require us to repurchase these notes or we may at our option elect to repurchase notes. These notes will mature in March 2032.

[3] The Convertible Senior Notes due 2032 will increase to their principal amount through accretion of non-cash interest charges through March 2018.