Long-Term Debt (Narrative) (Details) (USD $)	12 Months Ended						12 Months Ended		12 Months Ended				1 Months Ended			3 Months Ended	12 Months Ended			3 Months Ended	12 Months Ended			1 Months Ended	3 Months Ended	12 Months Ended					1 Months Ended	12 Months Ended					12 Months Ended		1 Months Ended						12 Months Ended
	Dec. 31, 2013 entity		Dec. 31, 2012	Dec. 31, 2011	Aug. 31, 2011	Sep. 30, 2013 Interest Rate Swaps [Member]	Dec. 31, 2013 Revolving Credit Facility Maturing June 2018 [Member]	Jun. 30, 2013 Revolving Credit Facility Maturing June 2018 [Member]	Dec. 31, 2013 Term Loan Maturing June 2018 [Member]		Jul. 31, 2013 Term Loan Maturing June 2018 [Member]	Jun. 30, 2013 Term Loan Maturing June 2018 [Member]	Jun. 30, 2013 Former Credit Facility [Member]	Feb. 28, 2013 Former Credit Facility [Member]	Feb. 28, 2013 Term Loan [Member]	Jun. 30, 2013 Term Loan [Member]	Dec. 31, 2013 Term Loan [Member]	Dec. 31, 2012 Term Loan [Member]		Jun. 30, 2013 Revolving Credit Facility [Member]	Dec. 31, 2013 Revolving Credit Facility [Member]	Dec. 31, 2012 Revolving Credit Facility [Member]		Jul. 31, 2013 Senior Unsecured Notes [Member]	Mar. 31, 2012 Senior Unsecured Notes [Member]	Dec. 31, 2013 Senior Unsecured Notes [Member]	Dec. 31, 2011 Senior Unsecured Notes [Member]	Dec. 31, 2012 Senior Unsecured Notes [Member]		Dec. 31, 2007 Senior Unsecured Notes [Member]	Mar. 31, 2012 2032 Notes [Member]	Dec. 31, 2013 2032 Notes [Member]		Dec. 31, 2012 2032 Notes [Member]		Mar. 06, 2012 2032 Notes [Member]	Dec. 31, 2013 MARAD Debt [Member]	Dec. 31, 2012 MARAD Debt [Member]	Feb. 28, 2013 2025 Notes [Member]	Dec. 31, 2012 2025 Notes [Member]		Mar. 31, 2012 2025 Notes [Member]	Jan. 31, 2009 2025 Notes [Member]	Mar. 31, 2005 2025 Notes [Member]	Dec. 31, 2013 2025 Notes [Member]	Dec. 31, 2012 2025 Notes [Member]		Dec. 31, 2011 2025 Notes [Member]	Dec. 31, 2013 Minimum [Member] Term Loan Maturing June 2018 [Member]	Dec. 31, 2013 Minimum [Member] Loans [Member]	Dec. 31, 2013 Minimum [Member] Loans [Member] London Interbank Offered Rate (LIBOR) [Member]	Dec. 31, 2013 Minimum [Member] Senior Unsecured Notes [Member]	Dec. 31, 2013 Maximum [Member] Loans [Member]	Dec. 31, 2013 Maximum [Member] Loans [Member] London Interbank Offered Rate (LIBOR) [Member]	Dec. 31, 2013 Maximum [Member] Senior Unsecured Notes [Member]	Dec. 31, 2013 Payment Period Two [Member] Term Loan Maturing June 2018 [Member]	Dec. 31, 2013 Payment Period One [Member] Term Loan Maturing June 2018 [Member]
Debt Instrument [Line Items]
Original borrowing capacity								$ 600,000,000				$ 300,000,000
Line Of Credit Facility Maximum Additional Commitments							200,000,000
Revolving credit facility, outstanding											300,000,000
Spread on Interest Rate																																					0.20%												2.50%	1.00%	2.00%		2.00%	3.00%
Commitment fee percentage							0.50%
Revolving credit facility available							584,200,000
Unsecured letters of credit							15,800,000
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
Number Of Foreign Subsidiaries	1
Amortization of deferred financing costs	5,187,000		9,086,000	8,910,000											2,900,000	600,000									2,000,000	2,100,000	900,000															300,000
Debt Instrument, Maturity Date, Description									June 2018								July 2015				July 2015					January 2016						March 2032					February 2027								December 2025
Repayments of debt													80,100,000							70,300,000				275,000,000	200,000,000		75,000,000															145,100,000
Repayments of term loans	374,681,000		12,569,000	130,691,000										318,400,000																									3,500,000	154,300,000
Senior Unsecured Notes amount issued																														550,000,000
Debt instrument interest rate																														9.50%	3.25%						4.93%							3.25%
Redemption Period																																																				30 days			60 days
Long-term debt, less current maturities	545,776,000		1,002,621,000						277,500,000	[1]																	475,000,000	275,000,000				173,484,000	[2]				94,792,000
Aggregate amount of debt payment	281,490,000		209,500,000	77,394,000																				282,000,000	213,500,000		77,400,000
Premium on debt extinguishment																								6,500,000	9,500,000		2,400,000															1,800,000
Accrued interest on notes																								500,000	4,000,000		800,000															1,100,000
Loss on early extinguishment of debt	12,100,000		17,127,000	2,354,000																					11,500,000	8,600,000																5,600,000
Long-term debt, Carrying Value	592,668,000		1,050,916,000						292,500,000									367,181,000	[3]			100,000,000	[3]					274,960,000	[4]		200,000,000	200,000,000	[5]	200,000,000	[5]		100,168,000	105,288,000		3,487,000	[6]			300,000,000		3,487,000	[6]
Proceeds from Issuance of Debt																															195,000,000
Convertible Senior Notes, shares of common stock																																39.9752
Base Principal Amount																																1,000
Per share conversion price																																$ 25.02		$ 25.02						$ 32.14					$ 32.14	$ 32.14		$ 32.14
Debt Instrument Convertible Conversion Premium Percentage																																				35.00%
Closing price per share																																				$ 18.53
Issuance Of Notes Percentage																																100.00%
Debt Instrument, Unamortized Discount	26,516,000	[7]	31,688,000																												35,400,000	26,516,000	[2],[7]										60,200,000
Expected life used to estimate fair value																																6 years											7 years 9 months
Effective interest rate																																6.90%													6.60%
Debt percentage guaranteed																																					50.00%
Debt instrument issued percentage																																												100.00%
Debt Instrument, Repurchase Amount																																										142,200,000
Accelerated amortization of debt discount	5,172,000		9,729,000	8,973,000																																						3,500,000
Deferred financing costs	10,954,000		7,580,000	9,311,000
Notional Amount of Foreign Currency Derivatives						148,100,000
Notional Amount of Derivatives					200,000,000
Repayment of revolving credit facility	$ 147,617,000			$ 109,400,000
Debt Instrument, Convertible, Conversion Price																																$ 25.02		$ 25.02						$ 32.14					$ 32.14	$ 32.14		$ 32.14
Debt Instrument, Convertible, Stock Price Trigger																																$ 32.53		$ 32.53
Incremental Common Shares Attributable to Conversion of Debt Securities																																0		0												0		0

[1] The amount reflects the borrowings made in July 2013 (see Credit Agreement discussion above).

[2] Beginning in March 2018, the holders of the 2032 Notes 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] Relates to the term loans and revolving credit facility under our former credit agreement, which was terminated in June 2013.

[4] We redeemed our remaining Senior Unsecured Notes in July 2013.

[5] Carrying value excludes the related unamortized debt discount of $26.5 million at December 31, 2013.

[6] This remaining amount was repurchased by us in February 2013.

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