Fair Value Measurements Fair Values Measured on Recurring Basis (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013		Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted cash	$ 2,956		$ 10,559
Long-term Debt	1,591,834		1,120,052
Current maturities of long-term debt	75,463		150,000
Carrying Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	343,581		280,596
Restricted cash	2,956	[1]	10,559	[1]
Long-term Debt	1,591,834		1,120,052
Current maturities of long-term debt	75,463		150,000
Carrying Value | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	(9,286)	[2]	0	[2]
Carrying Value | Fair Value, Measurements, Recurring [Member] | Energy Related Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fuel contracts	69	[2]	0	[2]
Carrying Value | Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	(1,065)	[2]	0	[2]
Carrying Value | Fair Value, Measurements, Recurring [Member] | Foreign Exchange Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	(716)	[2]	0	[2]
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	343,581		280,596
Restricted cash	2,956	[1]	10,559	[1]
Long-term Debt	0		0
Current maturities of long-term debt	0		0
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 1 | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	0	[2]	0	[2]
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 1 | Fair Value, Measurements, Recurring [Member] | Energy Related Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fuel contracts	0	[2]	0	[2]
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 1 | Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	0	[2]	0	[2]
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 1 | Fair Value, Measurements, Recurring [Member] | Foreign Exchange Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	0	[2]	0	[2]
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0		0
Restricted cash	0	[1]	0	[1]
Long-term Debt	1,718,249		1,250,341
Current maturities of long-term debt	75,463		150,000
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 2 | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps	(9,286)	[2]	0	[2]
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 2 | Fair Value, Measurements, Recurring [Member] | Energy Related Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fuel contracts	69	[2]	0	[2]
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 2 | Fair Value, Measurements, Recurring [Member] | Foreign Exchange Contract [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	(1,065)	[2]	0	[2]
Estimate of Fair Value, Fair Value Disclosure [Member] | Level 2 | Fair Value, Measurements, Recurring [Member] | Foreign Exchange Option [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Foreign currency contracts	$ (716)		$ 0	[2]

[1] Restricted cash is recorded in “Other Assets” and represents the proceeds from LKE sales deposited with a third-party intermediary.

[2] See Note 9 — Derivative Financial Instruments and Hedging Activities for information regarding the Balance Sheet classification of the Company’s derivative financial instruments.