Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 440,576	$ 442,845	$ 436,393	$ 445,684	$ 464,134	$ 474,935	$ 463,331	$ 447,385	$ 1,765,498	$ 1,849,785	$ 1,793,087
EXPENSES:
Operating									1,249,537	1,275,586	1,256,128
General and administrative									107,822	107,027	103,936
Depreciation and amortization									147,129	166,746	151,514
Asset impairments									614		955
Restructuring charges										4,010
Costs and Expenses, Total									1,505,102	1,553,369	1,512,533
OPERATING INCOME	65,263	60,815	65,279	69,039	80,359	73,953	77,176	64,928	260,396	296,416	280,554
OTHER (INCOME) EXPENSE:
Interest expense, net									68,535	67,755	49,696
Expenses associated with debt refinancing transactions											701
Other (income) expense									(90)	489	(58)
Total non-operating expense (income)									68,445	68,244	50,339
INCOME BEFORE INCOME TAXES									191,951	228,172	230,215
Income tax expense									(13,911)	(8,253)	(8,361)
INCOME BEFORE EQUITY IN SUBSIDIARIES									178,040	219,919	221,854
NET INCOME	$ 41,340	$ 41,178	$ 45,475	$ 50,047	$ 60,689	$ 55,340	$ 57,583	$ 46,307	178,040	219,919	221,854
Reportable Legal Entities | Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES									1,194,690	1,182,765	1,184,878
EXPENSES:
Operating									914,443	904,750	889,203
General and administrative									36,964	35,440	33,248
Depreciation and amortization									87,694	84,842	82,745
Asset impairments									300
Restructuring charges										197
Costs and Expenses, Total									1,039,401	1,025,229	1,005,196
OPERATING INCOME									155,289	157,536	179,682
OTHER (INCOME) EXPENSE:
Interest expense, net									56,712	51,928	35,919
Expenses associated with debt refinancing transactions											701
Other (income) expense									(255)	995	232
Total non-operating expense (income)									56,457	52,923	36,852
INCOME BEFORE INCOME TAXES									98,832	104,613	142,830
Income tax expense									(1,765)	(1,896)	(1,541)
INCOME BEFORE EQUITY IN SUBSIDIARIES									97,067	102,717	141,289
Income from equity in subsidiaries									80,973	117,202	80,565
NET INCOME									178,040	219,919	221,854
Reportable Legal Entities | Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES									1,454,194	1,542,231	1,469,105
EXPENSES:
Operating									1,218,480	1,246,047	1,227,821
General and administrative									70,858	71,587	70,688
Depreciation and amortization									59,435	81,904	68,769
Asset impairments									314		955
Restructuring charges										3,813
Costs and Expenses, Total									1,349,087	1,403,351	1,368,233
OPERATING INCOME									105,107	138,880	100,872
OTHER (INCOME) EXPENSE:
Interest expense, net									11,823	15,827	13,777
Other (income) expense									103	(548)	(414)
Total non-operating expense (income)									11,926	15,279	13,363
INCOME BEFORE INCOME TAXES									93,181	123,601	87,509
Income tax expense									(12,146)	(6,357)	(6,820)
INCOME BEFORE EQUITY IN SUBSIDIARIES									81,035	117,244	80,689
NET INCOME									81,035	117,244	80,689
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES									(883,386)	(875,211)	(860,896)
EXPENSES:
Operating									(883,386)	(875,211)	(860,896)
Costs and Expenses, Total									(883,386)	(875,211)	(860,896)
OTHER (INCOME) EXPENSE:
Other (income) expense									62	42	124
Total non-operating expense (income)									62	42	124
INCOME BEFORE INCOME TAXES									(62)	(42)	(124)
INCOME BEFORE EQUITY IN SUBSIDIARIES									(62)	(42)	(124)
Income from equity in subsidiaries									(80,973)	(117,202)	(80,565)
NET INCOME									$ (81,035)	$ (117,244)	$ (80,689)