Income Taxes Deferred tax assets and liabilties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Abstract]
Current Federal Tax Expense (Benefit)	$ 33,364	$ 6,860	$ 30,560
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	562	478
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	9,212	8,969
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	529	677
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Self Insurance	28,159	25,395
Deferred Tax Assets, Operating Loss Carryforwards	1,688	3,241
Deferred Tax Assets, Tax Deferred Expense	4,262	4,595
Deferred Tax Assets, Other	387	772
Deferred Tax Assets, Gross	44,799	44,127
Deferred Tax Assets, Valuation Allowance	0	0
Deferred Tax Assets, Net	44,799	44,127
Deferred Tax Liabilities, Property, Plant and Equipment	(133,720)	(125,611)
Deferred Tax Liabilities, Goodwill and Intangible Assets	(3,725)	(2,385)
Deferred Tax Liabilities, Deferred Expense	(2,810)	(2,969)
Deferred Income Tax Liabilities	(140,255)	(130,965)
Deferred Tax Liabilities, Net	$ (95,456)	$ (86,838)