Income Taxes (Tables)

12 Months Ended

Dec. 31, 2013

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:

	2013			2012
	(in thousands)
Deferred income tax assets:
Allowance for doubtful accounts	$	291		$	305
Accrued expenses	6,980			6,655
Stock-based compensation	648			579
Insurance accruals	26,000			27,549
Unrealized loss on available-for-sale investments	—			449
Indirect tax benefits of unrecognized tax benefits	4,846			5,658
Other	1,889			1,011
Total gross deferred tax assets	40,654			42,206
Less valuation allowance	—			(449		)
Net deferred tax assets	40,654			41,757
Deferred income tax liabilities:
Property and equipment	(85,849		)	(77,177		)
Goodwill	(1,835		)	(1,351		)
Prepaid expenses	(741		)	(738		)
	(88,425		)	(79,266		)
Net deferred tax liability	$	(47,771	)	$	(37,509	)

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, 2013 and 2012 as follows:

	2012			2011
	(in thousands)
Current assets, net	$	14,177		$	13,797
Long-term liabilities, net	(61,948		)	(51,306		)
	$	(47,771	)	$	(37,509	)

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

Income tax expense consists of the following:

	2013		2012			2011
	(in thousands)
Current income taxes:
Federal	$	30,560	$	38,148		20,460
State	1,152		1,636			2,195
	31,712		39,784			22,655
Deferred income taxes:
Federal	7,192		(5,890		)	16,587
State	3,070		140			(1,844		)
	10,262		(5,750		)	14,743
Total	$	41,974	$	34,034		$	37,398

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:

	2013			2012			2011
	(in thousands)
Federal tax at statutory rate (35%)	$	39,395		$	33,451		37,565
State taxes, net of federal benefit	3,242			1,554			981
Non-taxable interest income	(20		)	(48		)	(104		)
Uncertain income tax penalties and interest, net	(766		)	(616		)	(1,159		)
Other	123			(307		)	115
	$	41,974		$	34,034		$	37,398

Reconciliation of Unrecognized Tax Benefits [Table Text Block]

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

	2013			2012
	(in thousands)
Balance at January 1,	$	15,723		$	16,062
Additions based on tax positions related to current year	843			1,146
Additions for tax positions of prior years	616			1,075
Reductions for tax positions of prior years	(300		)	(134		)
Reductions due to lapse of applicable statute of limitations	(1,984		)	(2,426		)
Settlements	(1,466		)	—
Balance at December 31,	$	13,432		$	15,723