CONDENSED CONSOLIDATING FINANCIAL INFORMATION - Condensed Consolidating Statements of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Condensed Financial Statements, Captions [Line Items]
Operating revenues, net	$ 195,543	$ 160,554	$ 374,511	$ 298,605
Expenses:
Direct expenses	159,494	134,088	307,697	252,790
Selling, general and administrative expenses	10,024	9,672	18,290	18,508
Total operating expenses	169,518	143,760	325,987	271,298
Gain on disposal of assets, net	(14,701)	(679)	(14,676)	(690)
Impairment of assets	421		421
Equity in loss of unconsolidated affiliate	596		1,083
Operating income	39,709	17,473	61,696	27,997
Interest expense	7,257	7,440	14,666	14,640
Other income, net	(73)	(57)	(225)	(363)
Total expenses	7,184	7,383	14,441	14,277
Earnings before income taxes	32,525	10,090	47,255	13,720
Income tax expense	13,009	4,036	18,901	5,488
Net earnings	19,516	6,054	28,354	8,232
Parent Company Only (issuer) [Member]
Condensed Financial Statements, Captions [Line Items]
Operating revenues, net	116,808	102,270	229,293	194,368
Expenses:
Direct expenses	96,106	88,551	186,992	167,815
Selling, general and administrative expenses	8,022	7,861	14,354	14,947
Management fees	(5,809)	(2,331)	(5,809)	(4,169)
Total operating expenses	98,319	94,081	195,537	178,593
Gain on disposal of assets, net	(14,701)	(679)	(14,676)	(690)
Equity in loss of unconsolidated affiliate	596		1,083
Operating income	32,594	8,868	47,349	16,465
Equity in net income of consolidated subsidiaries	(4,522)	(5,156)	(8,861)	(6,912)
Interest expense	7,257	7,428	14,666	14,628
Other income, net	(73)	(57)	(225)	(363)
Total expenses	2,662	2,215	5,580	7,353
Earnings before income taxes	29,932	6,653	41,769	9,112
Income tax expense	10,163	599	13,162	880
Net earnings	19,769	6,054	28,607	8,232
Guarantor Subsidiaries [Member]
Condensed Financial Statements, Captions [Line Items]
Operating revenues, net	78,735	58,284	145,218	104,237
Expenses:
Direct expenses	63,388	45,537	120,705	84,975
Selling, general and administrative expenses	2,002	1,811	3,936	3,561
Management fees	5,809	2,331	5,809	4,169
Total operating expenses	71,199	49,679	130,450	92,705
Impairment of assets	421		421
Operating income	7,115	8,605	14,347	11,532
Interest expense		12		12
Total expenses		12		12
Earnings before income taxes	7,115	8,593	14,347	11,520
Income tax expense	2,846	3,437	5,739	4,608
Net earnings	4,269	5,156	8,608	6,912
Eliminations [Member]
Expenses:
Equity in net income of consolidated subsidiaries	4,522	5,156	8,861	6,912
Total expenses	4,522	5,156	8,861	6,912
Earnings before income taxes	(4,522)	(5,156)	(8,861)	(6,912)
Net earnings	$ (4,522)	$ (5,156)	$ (8,861)	$ (6,912)