Long-Term Debt (Narrative) (Details) (USD $)	12 Months Ended					12 Months Ended				12 Months Ended			12 Months Ended					12 Months Ended					12 Months Ended					12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Multi-Currency Line Of Credit [Member]	Dec. 31, 2013 Domestic And Multi-Currency Line Of Credit Up To $100,000 Due 2013 [Member]	Dec. 31, 2013 Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member] PCN	Dec. 31, 2012 Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member] PCN	Dec. 31, 2013 Variable Rate Senior Unsecured Note Due 2018 [Member]	Dec. 31, 2012 Variable Rate Senior Unsecured Note Due 2018 [Member]	Dec. 31, 2013 5.75% Senior Unsecured Notes Due 2018	May 15, 2013 5.75% Senior Unsecured Notes Due 2018	Dec. 31, 2012 5.75% Senior Unsecured Notes Due 2018	Dec. 31, 2013 5.25% Convertible Senior Notes Due 2029 [Member]	Dec. 31, 2012 5.25% Convertible Senior Notes Due 2029 [Member]	Dec. 31, 2011 5.25% Convertible Senior Notes Due 2029 [Member]	Dec. 31, 2013 Letter Of Credit Facility [Member]	Dec. 31, 2013 Standby Letters Of Credit [Member]	Dec. 31, 2013 Series A and B Notes [Member] NN	Dec. 31, 2013 Series A Notes [Member] PN	Dec. 31, 2013 Series B Notes [Member] PN	Dec. 31, 2013 LIBOR [Member] Variable Rate Senior Unsecured Note Due 2018 [Member]	Dec. 31, 2013 Agent Base Rate [Member] Variable Rate Senior Unsecured Note Due 2018 [Member]	Dec. 31, 2013 Minimum [Member] Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member]	Dec. 31, 2012 Minimum [Member] Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member]	Dec. 31, 2013 Minimum [Member] Series A and B Notes [Member]	Dec. 31, 2013 Minimum [Member] LIBOR [Member] Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member]	Dec. 31, 2013 Minimum [Member] Agent Base Rate [Member] Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member]	Dec. 31, 2013 Maximum [Member] Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member]	Dec. 31, 2012 Maximum [Member] Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member]	Dec. 31, 2013 Maximum [Member] LIBOR [Member] Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member]	Dec. 31, 2013 Maximum [Member] Agent Base Rate [Member] Domestic and Multi-Currency Line of Credit Due Two Thousand Eightteen [Member]
Debt Instrument [Line Items]
Maximum borrowing capacity				$ 50,000,000	$ 100,000,000	$ 280,000,000
Debt instrument maturity, year						2018		2018		2018			2029
Debt Instrument, Face Amount								50,000,000		300,000,000								52,000,000	47,000,000	5,000,000
Debt instrument basis spread on variable rate																					3.50%	2.00%				2.00%	0.50%			3.25%	1.75%
Weighted average interest rate						3.30%	3.06%	3.69%	3.75%
Commitment fee percentage						0.50%																	0.25%					0.50%
Debt Instrument, Periodic Payment, Principal								2,100,000										9,400,000		700,000
Number Of Pricing Tranches						3	3
Letter of credit facility, amount																20,000,000	17,600,000
Debt instrument, maturity date								Mar. 31, 2018		May 15, 2018			May 15, 2029						Aug. 28, 2019	Aug. 28, 2022
Debt instrument maturity days																							3 days	2 days				31 days	31 days
Debt Issurance Cost Amortization Period, in years								5 years		5 years
Debt Instrument, Issuance Date						Mar. 30, 2011				May 15, 2013			May 19, 2009					Aug. 28, 2012
Debt Instrument, Date of First Required Payment																			Aug. 28, 2015	Aug. 28, 2016
Debt facility issuance costs								1,800,000		8,600,000			3,900,000
Aggregate principal amount of convertible senior notes													115,000,000
Debt instrument, interest rate										5.75%			5.25%						6.00%	6.58%
Conversion rate of notes (in shares)													39.2157
Conversion price per share													$ 25.50
Repurchase price as percentage on principal amount													100.00%
Long Term Debt	739,989,000	578,330,000				193,717,000	301,011,000	33,333,000	41,667,000	300,000,000		0	101,757,000	110,197,000
Unamortized discount													1,200,000	4,800,000
Interest expenses													9,200,000	9,200,000	8,900,000
Amortization of debt discount	6,206,000	3,811,000	3,566,000										3,300,000	3,200,000	2,900,000
Contractual interest expenses													5,900,000	6,000,000	6,000,000
Effective interest rate													8.46%	8.46%
Convertible notes, if-converted value in excess of principal amount													49,700,000
Carrying amount of equity component recorded as additional paid-in capital													1,800,000	9,400,000
Numbers Of Notes Series																		2
Debt Instrument, Frequency of Periodic Payment								Quarterly										Annually
Number Of Payments																			5	7
Note Redeem Rate										100.00%
Note Repurchase Rate										101.00%
Repayments of Long-term Debt													19,800,000												1,000,000
Loss on extinguishment of debt													600,000
Original principal amount of repurshased notes													12,000,000
Line Of Credit Facility Amount Outstanding											$ 202,000,000