Fair Value Measurements Carrying Amounts and Fair Values (Details) (USD $) In Thousands, unless otherwise specified					3 Months Ended
	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2013 Cash, Cash Equivalents and Restricted Cash [Member]	Mar. 31, 2013 Borrowings [Member]	Mar. 31, 2013 Carrying Amount	Dec. 31, 2012 Carrying Amount	Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Level 1		Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Level 1		Mar. 31, 2013 Estimate of Fair Value, Fair Value Disclosure [Member] Level 2		Dec. 31, 2012 Estimate of Fair Value, Fair Value Disclosure [Member] Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and cash equivalents							$ 266,017	$ 280,596	$ 266,017		$ 280,596		$ 0		$ 0
Restricted cash	651	[1]	10,559	[1]					651	[1]	10,559	[1]	0	[1]	0	[1]
Current maturities of long-term debt	(50,000)		(150,000)				(50,000)	(150,000)	0		0		(50,000)		(150,000)
Long-term debt	$ (1,150,471)		$ (1,120,052)				$ (1,150,471)	$ (1,120,052)	$ 0		$ 0		$ (1,307,144)		$ (1,250,341)
Fair Value Measurements, Valuation Techniques					The carrying amount is equal to fair market value	The fair value of fixed rate debt is based upon quoted market prices for debt with similar terms and maturities.

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