Condensed Consolidating Financial Information (Details 1) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Condensed Consolidating Statements of Operations
Operating revenues, net	$ 178,968	$ 138,051
Expenses:
Direct expenses	148,203	118,698
Selling, general and administrative expenses	8,266	8,840
Loss (gain) on disposal of assets, net	25	(11)
Equity in loss of unconsolidated affiliate	487
Total operating expenses	156,469	127,538
Operating income	21,987	10,524
Interest expense	7,409	7,200
Other (income) expense, net	(152)	(306)
Total expenses	7,257	6,894
Earnings before income taxes	14,730	3,630
Income tax expense	5,892	1,452
Net earnings	8,838	2,178
Parent Company Only [Member]
Condensed Consolidating Statements of Operations
Operating revenues, net	112,485	92,098
Expenses:
Direct expenses	90,885	79,260
Selling, general and administrative expenses	6,333	7,090
Management fees	(2,659)	(1,838)
Loss (gain) on disposal of assets, net	25	(11)
Equity in loss of unconsolidated affiliate	487
Total operating expenses	94,559	84,512
Operating income	17,414	7,597
Equity in net income of consolidated subsidiaries	(2,744)	(1,756)
Interest expense	7,409	7,200
Other (income) expense, net	(152)	(306)
Total expenses	4,513	5,138
Earnings before income taxes	12,901	2,459
Income tax expense	4,063	281
Net earnings	8,838	2,178
Guarantor Subsidiaries [Member]
Condensed Consolidating Statements of Operations
Operating revenues, net	66,483	45,953
Expenses:
Direct expenses	57,318	39,438
Selling, general and administrative expenses	1,933	1,750
Management fees	2,659	1,838
Total operating expenses	61,910	43,026
Operating income	4,573	2,927
Earnings before income taxes	4,573	2,927
Income tax expense	1,829	1,171
Net earnings	2,744	1,756
Eliminations [Member]
Expenses:
Equity in net income of consolidated subsidiaries	2,744	1,756
Total expenses	2,744	1,756
Earnings before income taxes	(2,744)	(1,756)
Net earnings	$ (2,744)	$ (1,756)