Income Taxes (Tables)

12 Months Ended

Dec. 31, 2016

Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]

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

Deferred tax assets and liabilities as of December 31 are as follows:

	2016			2015
	(in thousands)
Deferred income tax assets:
Allowance for doubtful accounts	$	559		$	562
Accrued expenses	9,275			9,212
Stock-based compensation	254			529
Insurance accruals	29,190			28,159
State net operating loss carryforward	451			1,688
Indirect tax benefits of unrecognized tax benefits	3,334			4,262
Other	2			387
Total gross deferred tax assets	43,065			44,799
Less valuation allowance	—			—
Net deferred tax assets	43,065			44,799
Deferred income tax liabilities:
Property and equipment	(122,367		)	(133,720		)
Goodwill	(9,857		)	(3,725		)
Prepaid expenses	(1,713		)	(2,810		)
	(133,937		)	(140,255		)
Net deferred tax liability	$	(90,872	)	$	(95,456	)

Summary of Deferred Tax Assets (Liabilities) by Balance Sheet Classification [Table Text Block]

The deferred tax amounts above have been classified in the accompanying consolidated balance sheets at December 31, 2016 and 2015 as follows:

	2016			2015
	(in thousands)
Current assets, net	$	—		$	16,662
Noncurrent assets, net	3,785			—
Long-term liabilities, net	(94,657		)	(112,118		)
	$	(90,872	)	$	(95,456	)

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

Income tax expense consists of the following:

	2016			2015		2014
	(in thousands)
Current income taxes:
Federal	$	34,664		$	33,364	$	6,860
State	454			2,703		855
	35,118			36,067		7,715
Deferred income taxes:
Federal	(5,291		)	5,170		36,706
State	(164		)	2,478		2,362
	(5,455		)	7,648		39,068
Total	$	29,663		$	43,715	$	46,783

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

The income tax provision differs from the amount determined by applying the U.S. federal tax rate as follows:

	2016			2015			2014
	(in thousands)
Federal tax at statutory rate (35%)	$	30,117		$	40,870		$	46,066
State taxes, net of federal benefit	1,135			4,022			2,737
Non-taxable interest income	(7		)	(6		)	(7		)
Uncertain income tax penalties and interest, net	(1,473		)	(1,006		)	(993		)
Other	(109		)	(165		)	(1,020		)
	$	29,663		$	43,715		$	46,783

Reconciliation of Unrecognized Tax Benefits [Table Text Block]

A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows:

	2016			2015
	(in thousands)
Balance at January 1,	$	11,569		$	12,632
Additions based on tax positions related to current year	592			954
Additions for tax positions of prior years	—			—
Reductions for tax positions of prior years	(108		)	(90		)
Reductions due to lapse of applicable statute of limitations	(3,302		)	(1,927		)
Settlements	—			—
Balance at December 31,	$	8,751		$	11,569