Fair Value Measurements Carrying Amounts and Fair Values (Details) (USD $) In Thousands, unless otherwise specified															12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Carrying Amount		Dec. 31, 2011 Carrying Amount		Dec. 31, 2012 Fair Value, Level 1 Fair Value		Dec. 31, 2011 Fair Value, Level 1 Fair Value		Dec. 31, 2012 Fair Value, Level 2 Fair Value		Dec. 31, 2011 Fair Value, Level 2 Fair Value		Dec. 31, 2012 Cash, Cash Equivalents and Restricted Cash [Member]	Dec. 31, 2012 Borrowings [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value Measurements, Valuation Techniques															Cash and cash equivalents and Restricted cash — The carrying amount is equal to fair market value.	Debt — The fair value of fixed rate debt is based upon quoted market prices for debt with similar terms and maturities.
Cash and cash equivalents			$ 280,596		$ 78,603		$ 280,596		$ 78,603		$ 0		$ 0
Current maturities of long-term debt	(150,000)	(28,110)	(150,000)		(28,110)		0		0		(150,000)		(29,319)
Restricted Cash	10,600	0	10,559	[1]	0	[1]	10,559	[1]	0	[1]	0	[1]	0	[1]
Long-term debt	$ (1,120,052)	$ (819,229)	$ (1,120,052)		$ (819,229)		$ 0		$ 0		$ (1,250,341)		$ (994,851)

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