Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 442,845	$ 474,935	$ 1,324,922	$ 1,385,651
EXPENSES:
Operating	316,865	326,349	940,065	956,713
General and administrative	28,303	27,699	79,546	81,543
Depreciation and amortization	36,507	42,924	109,564	127,328
Asset impairments	355		614
Restructuring charges		4,010		4,010
Costs and Expenses, Total	382,030	400,982	1,129,789	1,169,594
OPERATING INCOME	60,815	73,953	195,133	216,057
OTHER (INCOME) EXPENSE:
Interest expense, net	17,029	16,937	50,141	51,277
Other (income) expense	(65)	54	(108)	103
Total non-operating expense (income)	16,964	16,991	50,033	51,380
INCOME BEFORE INCOME TAXES	43,851	56,962	145,100	164,677
Income tax expense	(2,673)	(1,622)	(8,400)	(5,447)
INCOME BEFORE EQUITY IN SUBSIDIARIES	41,178	55,340	136,700	159,230
NET INCOME	41,178	55,340	136,700	159,230
Reportable Legal Entities | Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES	297,856	298,659	885,271	876,697
EXPENSES:
Operating	231,528	230,244	679,458	676,997
General and administrative	9,823	9,326	26,630	27,352
Depreciation and amortization	22,147	21,321	65,206	63,267
Asset impairments	300		300
Restructuring charges		197		197
Costs and Expenses, Total	263,798	261,088	771,594	767,813
OPERATING INCOME	34,058	37,571	113,677	108,884
OTHER (INCOME) EXPENSE:
Interest expense, net	14,046	12,975	41,219	38,845
Other (income) expense	(96)	115	(248)	516
Total non-operating expense (income)	13,950	13,090	40,971	39,361
INCOME BEFORE INCOME TAXES	20,108	24,481	72,706	69,523
Income tax expense	(541)	(512)	(1,711)	(1,393)
INCOME BEFORE EQUITY IN SUBSIDIARIES	19,567	23,969	70,995	68,130
Income from equity in subsidiaries	21,611	31,371	65,705	91,100
NET INCOME	41,178	55,340	136,700	159,230
Reportable Legal Entities | Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES	368,507	398,617	1,094,805	1,162,834
EXPENSES:
Operating	308,855	318,446	915,761	933,596
General and administrative	18,480	18,373	52,916	54,191
Depreciation and amortization	14,360	21,603	44,358	64,061
Asset impairments	55		314
Restructuring charges		3,813		3,813
Costs and Expenses, Total	341,750	362,235	1,013,349	1,055,661
OPERATING INCOME	26,757	36,382	81,456	107,173
OTHER (INCOME) EXPENSE:
Interest expense, net	2,983	3,962	8,922	12,432
Other (income) expense	21	(57)	109	(401)
Total non-operating expense (income)	3,004	3,905	9,031	12,031
INCOME BEFORE INCOME TAXES	23,753	32,477	72,425	95,142
Income tax expense	(2,132)	(1,110)	(6,689)	(4,054)
INCOME BEFORE EQUITY IN SUBSIDIARIES	21,621	31,367	65,736	91,088
NET INCOME	21,621	31,367	65,736	91,088
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES	(223,518)	(222,341)	(655,154)	(653,880)
EXPENSES:
Operating	(223,518)	(222,341)	(655,154)	(653,880)
Costs and Expenses, Total	(223,518)	(222,341)	(655,154)	(653,880)
OTHER (INCOME) EXPENSE:
Other (income) expense	10	(4)	31	(12)
Total non-operating expense (income)	10	(4)	31	(12)
INCOME BEFORE INCOME TAXES	(10)	4	(31)	12
INCOME BEFORE EQUITY IN SUBSIDIARIES	(10)	4	(31)	12
Income from equity in subsidiaries	(21,611)	(31,371)	(65,705)	(91,100)
NET INCOME	$ (21,621)	$ (31,367)	$ (65,736)	$ (91,088)