Condensed Consolidating Statement of Operations (Unaudited) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 491,101	$ 484,064
EXPENSES:
Operating	362,315	345,832
General and administrative	31,279	29,445
Depreciation and amortization	37,952	35,523
Asset impairments	536
Costs and Expenses, Total	432,082	410,800
OPERATING INCOME	59,019	73,264
OTHER (INCOME) EXPENSE:
Interest expense, net	22,538	21,436
Other (income) expense	(533)	4
Total non-operating expense (income)	22,005	21,440
INCOME BEFORE INCOME TAXES	37,014	51,824
Income tax expense	(3,776)	(2,484)
INCOME BEFORE EQUITY IN SUBSIDIARIES	33,238	49,340
NET INCOME	33,238	49,340
Net income attributable to non-controlling interest	(1,181)
NET INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS	32,057	49,340
Reportable Legal Entities | Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES	336,062	335,212
EXPENSES:
Operating	267,851	257,493
General and administrative	10,168	10,028
Depreciation and amortization	23,483	23,284
Asset impairments	404
Costs and Expenses, Total	301,906	290,805
OPERATING INCOME	34,156	44,407
OTHER (INCOME) EXPENSE:
Interest expense, net	19,123	18,286
Other (income) expense	(490)	(68)
Total non-operating expense (income)	18,633	18,218
INCOME BEFORE INCOME TAXES	15,523	26,189
Income tax expense	(275)	(529)
INCOME BEFORE EQUITY IN SUBSIDIARIES	15,248	25,660
Income from equity in subsidiaries	17,990	23,680
NET INCOME	33,238	49,340
NET INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS	33,238
Reportable Legal Entities | Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES	405,482	392,077
EXPENSES:
Operating	350,872	334,995
General and administrative	21,111	19,417
Depreciation and amortization	11,310	10,315
Asset impairments	132
Costs and Expenses, Total	383,425	364,727
OPERATING INCOME	22,057	27,350
OTHER (INCOME) EXPENSE:
Interest expense, net	1,638	1,453
Other (income) expense	(75)	40
Total non-operating expense (income)	1,563	1,493
INCOME BEFORE INCOME TAXES	20,494	25,857
Income tax expense	(416)	(1,955)
INCOME BEFORE EQUITY IN SUBSIDIARIES	20,078	23,902
NET INCOME	20,078	23,902
NET INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS	20,078
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
REVENUES	9,047	5,723
EXPENSES:
Operating	3,082	2,292
Depreciation and amortization	3,159	1,924
Costs and Expenses, Total	6,241	4,216
OPERATING INCOME	2,806	1,507
OTHER (INCOME) EXPENSE:
Interest expense, net	1,777	1,697
Other (income) expense	32	32
Total non-operating expense (income)	1,809	1,729
INCOME BEFORE INCOME TAXES	997	(222)
Income tax expense	(3,085)
INCOME BEFORE EQUITY IN SUBSIDIARIES	(2,088)	(222)
NET INCOME	(2,088)	(222)
Net income attributable to non-controlling interest	(1,181)
NET INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS	(3,269)
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES	(259,490)	(248,948)
EXPENSES:
Operating	(259,490)	(248,948)
Costs and Expenses, Total	(259,490)	(248,948)
OTHER (INCOME) EXPENSE:
Income from equity in subsidiaries	(17,990)	(23,680)
NET INCOME	(17,990)	$ (23,680)
NET INCOME ATTRIBUTABLE TO COMMON STOCKHOLDERS	$ (17,990)