Income Taxes Deferred tax assets and liabilties (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes [Abstract]
Current Federal Tax Expense (Benefit)	$ 34,664	$ 33,364	$ 6,860
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	559	562
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Accrued Liabilities	9,275	9,212
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	254	529
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Self Insurance	29,190	28,159
Deferred Tax Assets, Operating Loss Carryforwards	451	1,688
Deferred Tax Assets, Tax Deferred Expense	3,334	4,262
Deferred Tax Assets, Other	2	387
Deferred Tax Assets, Gross	43,065	44,799
Deferred Tax Assets, Valuation Allowance	0	0
Deferred Tax Assets, Net	43,065	44,799
Deferred Tax Liabilities, Property, Plant and Equipment	(122,367)	(133,720)
Deferred Tax Liabilities, Goodwill and Intangible Assets	(9,857)	(3,725)
Deferred Tax Liabilities, Prepaid Expenses	1,713	2,810
Deferred Income Tax Liabilities	(133,937)	(140,255)
Deferred Tax Liabilities, Net	$ (90,872)	$ (95,456)