Note 7 - Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Notes Tables

Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]

	Years ended December 31,
	2015		2014		2013
Current:
Federal	$	160,235	$	130,761	$	144,299
State and local		22,306		19,705		18,811
		182,541		150,466		163,110
Deferred:
Federal		71,292		72,547		41,811
State and local		9,135		6,796		6,265
		80,427		79,343		48,076
Total tax expense	$	262,968	$	229,809	$	211,186

Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]

	Years ended December 31,
	2015			2014			2013
Income tax at federal statutory rate	$	241,571		$	211,610		$	193,749
State tax, net of federal effect		18,671			17,357			13,551
Nondeductible meals and entertainment		1,420			1,395			1,543
Change in effective state tax rate, net of federal benefit		1,761			256			3,708
Change in valuation allowance		-			-			(755	)
Other, net		(455	)		(809	)		(610	)
Total tax expense	$	262,968		$	229,809		$	211,186

Schedule of Deferred Tax Assets and Liabilities [Table Text Block]

	December 31,
	2015			2014
Deferred tax assets:
Insurance accruals	$	33,522		$	30,565
Allowance for doubtful accounts		2,335			2,291
Compensation accrual		13,991			15,260
Deferred compensation accrual		24,687			25,042
Federal benefit of state uncertain tax positions		12,751			12,268
Capital loss carry-forward		-			1,443
Other		4,036			3,954
Total gross deferred tax assets		91,322			90,823
Valuation allowance		(552	)		(1,994	)
Total deferred tax assets, net of valuation allowance		90,770			88,829
Deferred tax liabilities:
Plant and equipment, principally due to differences in depreciation		786,840			707,071
Prepaid permits and insurance, principally due to expensing for income tax purposes		33,064			30,012
Other		11,086			11,539
Total gross deferred tax liabilities		830,990			748,622
Net deferred tax liability	$	740,220		$	659,793

Summary of Positions for which Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Table Text Block]

	December 31,
	2015			2014			2013
Beginning balance	$	31.6		$	29.7		$	25.8
Additions based on tax positions related to the current year		9.4			8.2			7.0
Additions/(reductions) based on tax positions taken in prior years		(2.5	)		0.4			(1.2	)
Reductions due to settlements		(3.0	)		(3.7	)		(0.1	)
Reductions due to lapse of applicable statute of limitations		(3.5	)		(3.0	)		(1.8	)
Ending balance	$	32.0		$	31.6		$	29.7