Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Statements of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Condensed Income Statements, Captions [Line Items]
Operating revenues, net	$ 212,145		$ 195,543		$ 409,216		$ 374,511
Expenses:
Direct expenses	170,357		159,494		329,010		307,697
Selling, general and administrative expenses	11,660		10,024		20,988		18,290
Management fees
Total operating expenses	182,017		169,518		349,998		325,987
Loss (gain) on disposal of assets	242		(14,701)		1,315		(14,676)
Impairment of assets			421		0		421
Equity in loss of unconsolidated affiliate	65		596		106		1,083
Operating income	29,821		39,709		57,797		61,696
Equity in net income of consolidated subsidiaries
Interest expense	7,673		7,257		15,037		14,666
Loss on debt extinguishment	617				29,833
Other income, net	(169)		(73)		(260)		(225)
Total expenses	8,121		7,184		44,610		14,441
Earnings before income taxes	21,700		32,525		13,187		47,255
Income tax expense	8,332		13,009		5,140		18,901
Net earnings	13,368		19,516		8,047		28,354
Parent Company Only (issuer) [Member]
Condensed Income Statements, Captions [Line Items]
Operating revenues, net	122,392		116,808		246,746		229,293
Expenses:
Direct expenses	102,915		96,106		199,341		186,992
Selling, general and administrative expenses	8,629		8,022		15,710		14,354
Management fees	(3,590)		(5,809)		(6,499)		(5,809)
Total operating expenses	107,954		98,319		208,552		195,537
Loss (gain) on disposal of assets	1,199		(14,701)		1,315		(14,676)
Impairment of assets
Equity in loss of unconsolidated affiliate	65		596		106		1,083
Operating income	13,174		32,594		36,773		47,349
Equity in net income of consolidated subsidiaries	(10,111)		(4,522)		(12,846)		(8,861)
Interest expense	7,673		7,257		15,037		14,666
Loss on debt extinguishment	617				29,833
Other income, net	(169)		(73)		(260)		(225)
Total expenses	(1,990)		2,662		31,764		5,580
Earnings before income taxes	15,164		29,932		5,009		41,769
Income tax expense	1,796		10,163		(3,038)		(13,162)
Net earnings	13,368		19,769		8,047		28,607
Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Operating revenues, net	89,753	[1]	78,735	[1]	162,470	[1]	145,218	[1]
Expenses:
Direct expenses	67,442	[1]	63,388	[1]	129,669	[1]	120,705	[1]
Selling, general and administrative expenses	3,031	[1]	2,002	[1]	5,278	[1]	3,936	[1]
Management fees	3,590	[1]	5,809	[1]	6,499	[1]	5,809	[1]
Total operating expenses	74,063	[1]	71,199	[1]	141,446	[1]	130,450	[1]
Loss (gain) on disposal of assets	(957)	[1]		[1]		[1]
Impairment of assets			421	[1]			421	[1]
Equity in loss of unconsolidated affiliate		[1]		[1]		[1]
Operating income	16,647	[1]	7,115	[1]	21,024	[1]	14,347	[1]
Equity in net income of consolidated subsidiaries		[1]		[1]		[1]
Interest expense		[1]		[1]		[1]
Loss on debt extinguishment		[1]				[1]
Other income, net		[1]		[1]		[1]
Total expenses		[1]		[1]		[1]
Earnings before income taxes	16,647	[1]	7,115	[1]	21,024	[1]	14,347	[1]
Income tax expense	6,536	[1]	2,846	[1]	8,178	[1]	(5,739)	[1]
Net earnings	10,111	[1]	4,269	[1]	12,846	[1]	8,608	[1]
Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Operating revenues, net
Expenses:
Direct expenses
Selling, general and administrative expenses
Management fees
Total operating expenses
Loss (gain) on disposal of assets
Impairment of assets
Equity in loss of unconsolidated affiliate
Operating income
Equity in net income of consolidated subsidiaries	10,111		4,522		12,846		8,861
Interest expense
Loss on debt extinguishment
Other income, net
Total expenses	10,111		4,522		12,846		8,861
Earnings before income taxes	(10,111)		(4,522)		(12,846)		(8,861)
Income tax expense
Net earnings	$ (10,111)		$ (4,522)		$ (12,846)		$ (8,861)

[1] Foreign subsidiaries represent minor subsidiaries and are included in the guarantors' subsidiaries amounts.