Long-Term Debt (Narrative) (Details) (USD $)	3 Months Ended			3 Months Ended					0 Months Ended	3 Months Ended				0 Months Ended	3 Months Ended		0 Months Ended			3 Months Ended	0 Months Ended			3 Months Ended		0 Months Ended			3 Months Ended		0 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Mar. 31, 2014 Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member] PCN	Mar. 31, 2013 Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member] PCN	Dec. 31, 2013 Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]	May 10, 2013 Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]	May 10, 2013 Domestic And Multi-Currency Line Of Credit Up To $100,000 Due 2018 [Member]	May 10, 2013 Variable Rate Senior Unsecured Note Due 2018 [Member]	Mar. 31, 2014 Variable Rate Senior Unsecured Note Due 2018 [Member]	Dec. 31, 2013 Variable Rate Senior Unsecured Note Due 2018 [Member]	Mar. 31, 2013 Variable Rate Senior Unsecured Note Due 2018 [Member]	Mar. 30, 2011 Variable Rate Senior Unsecured Note Due 2018 [Member]	May 19, 2009 5.25% Convertible Senior Notes Due 2029 [Member]	Mar. 31, 2014 5.25% Convertible Senior Notes Due 2029 [Member]	Mar. 31, 2013 5.25% Convertible Senior Notes Due 2029 [Member]	May 15, 2013 5.75% $300 Million Senior Unsecured Notes	Mar. 31, 2014 5.75% $300 Million Senior Unsecured Notes	Mar. 30, 2011 Letter Of Credit Facility [Member]	Mar. 31, 2014 Standby Letters Of Credit [Member]	May 10, 2013 LIBOR [Member] Variable Rate Senior Unsecured Note Due 2018 [Member]	May 10, 2013 Agent's Base Rate [Member] Variable Rate Senior Unsecured Note Due 2018 [Member]	May 10, 2013 Minimum Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]	Mar. 31, 2014 Minimum Variable Rate Senior Unsecured Note Due 2018 [Member]	Mar. 31, 2013 Minimum Variable Rate Senior Unsecured Note Due 2018 [Member]	May 10, 2013 Minimum LIBOR [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]	May 10, 2013 Minimum Agent's Base Rate [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]	May 10, 2013 Maximum Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]	Mar. 31, 2014 Maximum Variable Rate Senior Unsecured Note Due 2018 [Member]	Mar. 31, 2013 Maximum Variable Rate Senior Unsecured Note Due 2018 [Member]	May 10, 2013 Maximum LIBOR [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]	May 10, 2013 Maximum Agent's Base Rate [Member] Domestic And Multi-Currency Line Of Credit Up To $280,000 Due 2018 [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity							$ 280,000,000	$ 100,000,000.0
Debt Instrument, Face Amount									50,000,000.0				50,000,000.0				300,000,000
Debt instrument basis spread on variable rate																				2.00%	3.50%	2.00%				2.00%	0.50%				3.25%	1.75%
Commitment fee, percentage				0.50%																			0.25%					0.50%
Weighted average interest rate				3.20%	3.04%	3.30%				3.69%	3.69%	3.75%
NumberOfPricingTranches				3	3
Debt instrument maturity days																								1 day	2 days				30 days	30 days
Debt instrument, maturity year									2018	2018
Debt Instrument, Periodic Payment, Principal									2,100,000
Debt instrument, maturity date									Mar. 31, 2018								May 15, 2018
Debt Issuance Costs					1,800,000										3,900,000		8,700,000
Debt Instrument, Issuance Date																	May 15, 2013
Debt instrument, interest rate														5.25%			5.75%
Note Redeem Rate																	100.00%
Note Repurchase Rate															100.00%		101.00%
Issurance Cost Amortization Period, in years																	5 years
Aggregate principal amount of convertible senior notes														115,000,000.0
Conversion rate of notes (in shares)														39.2157
Conversion Price Per Share														$ 25.50
Debt Instrument, Repurchased Face Amount															58,600,000
Repayments of Long-term Debt															89,500,000
Gain (Loss) on Repurchase of Debt Instrument															1,500,000
Long-term Debt	630,256,000	450,383,000	739,989,000							31,250,000	33,333,000	39,583,000			44,200,000	111,000,000
Debt Instrument, Unamortized Discount															200,000	4,000,000
Interest Expense, Debt															1,400,000	2,300,000
Amortization of Debt Discount (Premium)	1,213,000	1,320,000													500,000	800,000
Contractual interest expenses															800,000	1,500,000
Effective Interest Rate															8.46%
Debt Instrument, Convertible, If-converted Value in Excess of Principal															26,200,000
Adjustments to Additional Paid in Capital, Other															30,300,000
Adjustments to Additional Paid in Capital, Convertible Debt with Conversion Feature															(28,500,000)
Subsidiary Guarantors Ownership Percentage																		100.00%
Letter of credit facility, amount																			$ 20,000,000.0	$ 17,600,000
Debt Instrument Frequency Of Periodic Payment										Quarterly