Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

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:

	2017			2016
	(in thousands)
Deferred income tax assets:
Allowance for doubtful accounts	$	515		$	559
Accrued expenses	6,550			9,275
Stock-based compensation	156			254
Insurance accruals	18,225			29,190
State net operating loss carryforward	237			451
Indirect tax benefits of unrecognized tax benefits	1,278			3,334
Other	—			2
Total gross deferred tax assets	26,961			43,065
Less valuation allowance	—			—
Net deferred tax assets	26,961			43,065
Deferred income tax liabilities:
Property and equipment	(81,322		)	(122,367		)
Goodwill	(7,984		)	(9,857		)
Prepaid expenses	(1,406		)	(1,713		)
	(90,712		)	(133,937		)
Net deferred tax liability	$	(63,751	)	$	(90,872	)

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, 2017 and 2016 as follows:

	2017			2016
	(in thousands)
Noncurrent assets, net	$	1,737		$	3,785
Long-term liabilities, net	(65,488		)	(94,657		)
	$	(63,751	)	$	(90,872	)

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

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

	2017			2016			2015
	(in thousands)
Federal tax at statutory rate (35%)	$	22,574		$	30,117		$	40,870
State taxes, net of federal benefit	178			1,135			4,022
Non-taxable interest income	(7		)	(7		)	(6		)
Uncertain income tax penalties and interest, net	(1,208		)	(1,473		)	(1,006		)
Enacted federal tax rate change	(32,789		)	—			—
Other	577			(109		)	(165		)
	$	(10,675	)	$	29,663		$	43,715

Income tax expense consists of the following:

	2017			2016			2015
	(in thousands)
Current income taxes:
Federal	$	17,997		$	34,664		$	33,364
State	(1,495		)	454			2,703
	16,502			35,118			36,067
Deferred income taxes:
Federal	(28,020		)	(5,291		)	5,170
State	843			(164		)	2,478
	(27,177		)	(5,455		)	7,648
Total	$	(10,675	)	$	29,663		$	43,715

Reconciliation of Unrecognized Tax Benefits [Table Text Block]

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

	2017			2016
	(in thousands)
Balance at January 1,	$	8,751		$	11,569
Additions based on tax positions related to current year	135			592
Additions for tax positions of prior years	—			—
Reductions for tax positions of prior years	(331		)	(108		)
Reductions due to lapse of applicable statute of limitations	(2,699		)	(3,302		)
Settlements	(17		)	—
Balance at December 31,	$	5,839		$	8,751