Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 497,809	$ 508,522	$ 490,294	$ 484,064	$ 482,193	$ 462,728	$ 449,929	$ 440,916	$ 1,980,689	$ 1,835,766	$ 1,765,498
EXPENSES:
Operating									1,422,769	1,315,250	1,249,537
General and administrative									127,078	106,865	107,822
Depreciation and amortization									144,572	156,501	147,129
Contingent consideration for acquisition of businesses										6,085
Asset impairments							1,600		4,706	1,580	614
Costs and Expenses, Total									1,699,125	1,586,281	1,505,102
OPERATING INCOME	66,251	71,095	70,954	73,264	64,649	64,419	61,712	58,705	281,564	249,485	260,396
OTHER (INCOME) EXPENSE:
Interest expense, net									84,401	80,753	68,535
Expenses associated with debt refinancing transactions									602	1,016
Other (income) expense									(164)	156	(90)
Total non-operating expense (income)									84,839	81,925	68,445
INCOME BEFORE INCOME TAXES									196,725	167,560	191,951
Income tax expense									(7,839)	(8,353)	(13,911)
INCOME BEFORE EQUITY IN SUBSIDIARIES									188,886	159,207	178,040
NET INCOME	$ 41,974	$ 48,994	$ 48,578	$ 49,340	$ 41,239	$ 40,994	$ 39,197	$ 37,777	188,886	159,207	178,040
Reportable Legal Entities | Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES									1,363,562	1,279,991	1,194,690
EXPENSES:
Operating									1,065,596	994,505	914,443
General and administrative									42,680	36,409	36,964
Depreciation and amortization									93,575	92,702	87,694
Contingent consideration for acquisition of businesses										6,085
Asset impairments									4,706	1,580	300
Costs and Expenses, Total									1,206,557	1,131,281	1,039,401
OPERATING INCOME									157,005	148,710	155,289
OTHER (INCOME) EXPENSE:
Interest expense, net									71,969	67,340	56,712
Expenses associated with debt refinancing transactions									493	1,016
Other (income) expense									(363)	160	(255)
Total non-operating expense (income)									72,099	68,516	56,457
INCOME BEFORE INCOME TAXES									84,906	80,194	98,832
Income tax expense									(1,710)	(1,383)	(1,765)
INCOME BEFORE EQUITY IN SUBSIDIARIES									83,196	78,811	97,067
Income from equity in subsidiaries									105,690	80,396	80,973
NET INCOME									188,886	159,207	178,040
Reportable Legal Entities | Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES									1,627,226	1,514,503	1,454,194
EXPENSES:
Operating									1,381,676	1,284,616	1,218,480
General and administrative									84,398	70,456	70,858
Depreciation and amortization									43,231	61,206	59,435
Asset impairments											314
Costs and Expenses, Total									1,509,305	1,416,278	1,349,087
OPERATING INCOME									117,921	98,225	105,107
OTHER (INCOME) EXPENSE:
Interest expense, net									5,658	10,905	11,823
Expenses associated with debt refinancing transactions									109
Other (income) expense									72	(105)	103
Total non-operating expense (income)									5,839	10,800	11,926
INCOME BEFORE INCOME TAXES									112,082	87,425	93,181
Income tax expense									(6,129)	(6,970)	(12,146)
INCOME BEFORE EQUITY IN SUBSIDIARIES									105,953	80,455	81,035
NET INCOME									105,953	80,455	81,035
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
REVENUES									23,546	8,243
EXPENSES:
Operating									9,142	3,100
Depreciation and amortization									7,766	2,593
Costs and Expenses, Total									16,908	5,693
OPERATING INCOME									6,638	2,550
OTHER (INCOME) EXPENSE:
Interest expense, net									6,774	2,508
Other (income) expense									335	101
Total non-operating expense (income)									7,109	2,609
INCOME BEFORE INCOME TAXES									(471)	(59)
INCOME BEFORE EQUITY IN SUBSIDIARIES									(471)	(59)
NET INCOME									(471)	(59)
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES									(1,033,645)	(966,971)	(883,386)
EXPENSES:
Operating									(1,033,645)	(966,971)	(883,386)
Costs and Expenses, Total									(1,033,645)	(966,971)	(883,386)
OTHER (INCOME) EXPENSE:
Other (income) expense									(208)		62
Total non-operating expense (income)									(208)		62
INCOME BEFORE INCOME TAXES									208		(62)
INCOME BEFORE EQUITY IN SUBSIDIARIES									208		(62)
Income from equity in subsidiaries									(105,690)	(80,396)	(80,973)
NET INCOME									$ (105,482)	$ (80,396)	$ (81,035)