Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 482,193	$ 462,728	$ 449,929	$ 440,916	$ 440,576	$ 442,845	$ 436,393	$ 445,684	$ 1,835,766	$ 1,765,498	$ 1,849,785
EXPENSES:
Operating									1,315,250	1,249,537	1,275,586
General and administrative									106,865	107,822	107,027
Depreciation and amortization									156,501	147,129	166,746
Contingent consideration for acquisition of businesses									6,085
Asset impairments			1,600						1,580	614
Restructuring charges											4,010
Costs and Expenses, Total									1,586,281	1,505,102	1,553,369
OPERATING INCOME	64,649	64,419	61,712	58,705	65,263	60,815	65,279	69,039	249,485	260,396	296,416
OTHER (INCOME) EXPENSE:
Interest expense, net									80,753	68,535	67,755
Expenses associated with debt refinancing transactions									1,016
Other (income) expense									156	(90)	489
Total non-operating expense (income)									81,925	68,445	68,244
INCOME BEFORE INCOME TAXES									167,560	191,951	228,172
Income tax expense									(8,353)	(13,911)	(8,253)
INCOME BEFORE EQUITY IN SUBSIDIARIES									159,207	178,040	219,919
NET INCOME	$ 41,239	$ 40,994	$ 39,197	$ 37,777	$ 41,340	$ 41,178	$ 45,475	$ 50,047	159,207	178,040	219,919
Reportable Legal Entities | Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES									1,279,991	1,194,690	1,182,765
EXPENSES:
Operating									994,505	914,443	904,750
General and administrative									36,409	36,964	35,440
Depreciation and amortization									92,702	87,694	84,842
Contingent consideration for acquisition of businesses									6,085
Asset impairments									1,580	300
Restructuring charges											197
Costs and Expenses, Total									1,131,281	1,039,401	1,025,229
OPERATING INCOME									148,710	155,289	157,536
OTHER (INCOME) EXPENSE:
Interest expense, net									67,340	56,712	51,928
Expenses associated with debt refinancing transactions									1,016
Other (income) expense									160	(255)	995
Total non-operating expense (income)									68,516	56,457	52,923
INCOME BEFORE INCOME TAXES									80,194	98,832	104,613
Income tax expense									(1,383)	(1,765)	(1,896)
INCOME BEFORE EQUITY IN SUBSIDIARIES									78,811	97,067	102,717
Income from equity in subsidiaries									80,396	80,973	117,202
NET INCOME									159,207	178,040	219,919
Reportable Legal Entities | Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES									1,514,503	1,454,194	1,542,231
EXPENSES:
Operating									1,284,616	1,218,480	1,246,047
General and administrative									70,456	70,858	71,587
Depreciation and amortization									61,206	59,435	81,904
Asset impairments										314
Restructuring charges											3,813
Costs and Expenses, Total									1,416,278	1,349,087	1,403,351
OPERATING INCOME									98,225	105,107	138,880
OTHER (INCOME) EXPENSE:
Interest expense, net									10,905	11,823	15,827
Other (income) expense									(105)	103	(548)
Total non-operating expense (income)									10,800	11,926	15,279
INCOME BEFORE INCOME TAXES									87,425	93,181	123,601
Income tax expense									(6,970)	(12,146)	(6,357)
INCOME BEFORE EQUITY IN SUBSIDIARIES									80,455	81,035	117,244
NET INCOME									80,455	81,035	117,244
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
REVENUES									8,243
EXPENSES:
Operating									3,100
Depreciation and amortization									2,593
Costs and Expenses, Total									5,693
OPERATING INCOME									2,550
OTHER (INCOME) EXPENSE:
Interest expense, net									2,508
Other (income) expense									101
Total non-operating expense (income)									2,609
INCOME BEFORE INCOME TAXES									(59)
INCOME BEFORE EQUITY IN SUBSIDIARIES									(59)
NET INCOME									(59)
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES									(966,971)	(883,386)	(875,211)
EXPENSES:
Operating									(966,971)	(883,386)	(875,211)
Costs and Expenses, Total									(966,971)	(883,386)	(875,211)
OTHER (INCOME) EXPENSE:
Other (income) expense										62	42
Total non-operating expense (income)										62	42
INCOME BEFORE INCOME TAXES										(62)	(42)
INCOME BEFORE EQUITY IN SUBSIDIARIES										(62)	(42)
Income from equity in subsidiaries									(80,396)	(80,973)	(117,202)
NET INCOME									$ (80,396)	$ (81,035)	$ (117,244)