Federal and state income taxes Deferred Tax Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]
Deferred Tax Assets, Goodwill	$ 116,902	$ 135,572
Deferred Tax Assets, Operating Loss Carryforwards	11,099	10,893
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Benefits	7,871	9,009
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Reserves	6,424	9,481
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	16,444	13,961
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Compensated Absences	2,109	2,242
Deferred Tax Assets, Other	226	1,961
Deferred Tax Assets, Gross	161,075	183,119
Deferred Tax Liabilities, Property, Plant and Equipment	(157,185)	(148,335)
Deferred Tax Liabilities, Deferred Expense	(1,489)	(1,662)
Deferred Tax Liabilities, Other	(2,170)	0
Deferred Tax Liabilities	(160,844)	(149,997)
Deferred Tax Assets, Net	$ 231	$ 33,122