Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 474,935	$ 459,957	$ 1,385,651	$ 1,345,252
EXPENSES:
Operating	326,349	326,500	956,713	945,197
General and administrative	27,699	26,791	81,543	76,770
Depreciation and amortization	42,924	41,230	127,328	108,315
Asset impairments				955
Restructuring charges	4,010		4,010
Costs and Expenses	400,982	394,521	1,169,594	1,131,237
Operating income	73,953	65,436	216,057	214,015
OTHER (INCOME) EXPENSE:
Interest expense, net	16,937	11,764	51,277	33,715
Expenses associated with debt refinancing transactions		701		701
Other (income) expense	54	(363)	103	(353)
Total non-operating expense (income)	16,991	12,102	51,380	34,063
INCOME BEFORE INCOME TAXES	56,962	53,334	164,677	179,952
Income tax expense	(1,622)	(2,658)	(5,447)	(6,696)
INCOME BEFORE EQUITY IN SUBSIDIARIES	55,340	50,676	159,230	173,256
NET INCOME	55,340	50,676	159,230	173,256
Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES	298,659	294,578	876,697	899,992
EXPENSES:
Operating	230,244	226,020	676,997	669,653
General and administrative	9,326	8,226	27,352	23,725
Depreciation and amortization	21,321	20,623	63,267	60,967
Restructuring charges	197		197
Costs and Expenses	261,088	254,869	767,813	754,345
Operating income	37,571	39,709	108,884	145,647
OTHER (INCOME) EXPENSE:
Interest expense, net	12,975	7,739	38,845	24,420
Expenses associated with debt refinancing transactions		701		701
Other (income) expense	115	131	516	91
Total non-operating expense (income)	13,090	8,571	39,361	25,212
INCOME BEFORE INCOME TAXES	24,481	31,138	69,523	120,435
Income tax expense	(512)	(480)	(1,393)	(1,001)
INCOME BEFORE EQUITY IN SUBSIDIARIES	23,969	30,658	68,130	119,434
Income from equity in subsidiaries	31,371	20,018	91,100	53,822
NET INCOME	55,340	50,676	159,230	173,256
Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES	398,617	384,840	1,162,834	1,093,011
EXPENSES:
Operating	318,446	319,941	933,596	923,295
General and administrative	18,373	18,565	54,191	53,045
Depreciation and amortization	21,603	20,607	64,061	47,348
Asset impairments				955
Restructuring charges	3,813		3,813
Costs and Expenses	362,235	359,113	1,055,661	1,024,643
Operating income	36,382	25,727	107,173	68,368
OTHER (INCOME) EXPENSE:
Interest expense, net	3,962	4,025	12,432	9,295
Other (income) expense	(57)	(469)	(401)	(479)
Total non-operating expense (income)	3,905	3,556	12,031	8,816
INCOME BEFORE INCOME TAXES	32,477	22,171	95,142	59,552
Income tax expense	(1,110)	(2,178)	(4,054)	(5,695)
INCOME BEFORE EQUITY IN SUBSIDIARIES	31,367	19,993	91,088	53,857
NET INCOME	31,367	19,993	91,088	53,857
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES	(222,341)	(219,461)	(653,880)	(647,751)
EXPENSES:
Operating	(222,341)	(219,461)	(653,880)	(647,751)
Costs and Expenses	(222,341)	(219,461)	(653,880)	(647,751)
OTHER (INCOME) EXPENSE:
Other (income) expense	(4)	(25)	(12)	35
Total non-operating expense (income)	(4)	(25)	(12)	35
INCOME BEFORE INCOME TAXES	4	25	12	(35)
INCOME BEFORE EQUITY IN SUBSIDIARIES	4	25	12	(35)
Income from equity in subsidiaries	(31,371)	(20,018)	(91,100)	(53,822)
NET INCOME	$ (31,367)	$ (19,993)	$ (91,088)	$ (53,857)