Long-Term Debt And Other Long-Term Liabilities (Other Long-Term Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Long-term debt and other long-term liabilites [Abstract]
ARO liability	$ 146,159	$ 96,446	$ 69,265
Workers' compensation	18,517	17,026
Separation benefit plans	7,972	6,845
Gas balancing liability	3,838	3,263
Deferred compensation plan	2,779	2,463
Other liabilities	179,265	126,043
Less current portion	12,282	12,213
Other Liabilities, Noncurrent	$ 166,983	$ 113,830