Income Taxes (Tables)

12 Months Ended

Dec. 31, 2015

Income Tax Disclosure [Abstract]

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

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

	2015			2014
	(in thousands)
Deferred income tax assets:
Allowance for doubtful accounts	$	562		$	478
Accrued expenses	9,212			8,969
Stock-based compensation	529			677
Insurance accruals	28,159			25,395
State net operating loss carryforward	1,688			3,241
Indirect tax benefits of unrecognized tax benefits	4,262			4,595
Other	387			772
Total gross deferred tax assets	44,799			44,127
Less valuation allowance	—			—
Net deferred tax assets	44,799			44,127
Deferred income tax liabilities:
Property and equipment	(133,720		)	(125,611		)
Goodwill	(3,725		)	(2,385		)
Prepaid expenses	(2,810		)	(2,969		)
	(140,255		)	(130,965		)
Net deferred tax liability	$	(95,456	)	$	(86,838	)

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, 2015 and 2014 as follows:

	2015			2014
	(in thousands)
Current assets, net	$	16,662		$	14,767
Long-term liabilities, net	(112,118		)	(101,605		)
	$	(95,456	)	$	(86,838	)

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

Income tax expense consists of the following:

	2015		2014		2013
	(in thousands)
Current income taxes:
Federal	$	33,364	$	6,860	$	30,560
State	2,703		855		1,152
	36,067		7,715		31,712
Deferred income taxes:
Federal	5,170		36,706		7,192
State	2,478		2,362		3,070
	7,648		39,068		10,262
Total	$	43,715	$	46,783	$	41,974

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:

	2015			2014			2013
	(in thousands)
Federal tax at statutory rate (35%)	$	40,870		$	46,066		$	39,395
State taxes, net of federal benefit	4,022			2,737			3,242
Non-taxable interest income	(6		)	(7		)	(20		)
Uncertain income tax penalties and interest, net	(1,006		)	(993		)	(766		)
Other	(165		)	(1,020		)	123
	$	43,715		$	46,783		$	41,974

Reconciliation of Unrecognized Tax Benefits [Table Text Block]

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

	2015			2014
	(in thousands)
Balance at January 1,	$	12,632		$	13,432
Additions based on tax positions related to current year	954			983
Additions for tax positions of prior years	—			277
Reductions for tax positions of prior years	(90		)	—
Reductions due to lapse of applicable statute of limitations	(1,927		)	(2,060		)
Settlements	—			—
Balance at December 31,	$	11,569		$	12,632