Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 436,393	$ 463,331	$ 882,077	$ 910,716
EXPENSES:
Operating	307,897	316,446	623,200	630,364
General and administrative	26,417	27,364	51,243	53,844
Depreciation and amortization	36,800	42,345	73,057	84,404
Asset impairments			259
Costs and Expenses, Total	371,114	386,155	747,759	768,612
OPERATING INCOME	65,279	77,176	134,318	142,104
OTHER (INCOME) EXPENSE:
Interest expense, net	16,622	16,796	33,112	34,340
Other (income) expense	(60)	132	(43)	49
Total non-operating expense (income)	16,562	16,928	33,069	34,389
INCOME BEFORE INCOME TAXES	48,717	60,248	101,249	107,715
Income tax expense	(3,242)	(2,665)	(5,727)	(3,825)
INCOME BEFORE EQUITY IN SUBSIDIARIES	45,475	57,583	95,522	103,890
NET INCOME	45,475	57,583	95,522	103,890
Reportable Legal Entities | Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES	287,900	293,314	587,415	578,038
EXPENSES:
Operating	221,293	224,689	447,930	446,753
General and administrative	8,471	8,832	16,807	18,026
Depreciation and amortization	21,711	21,055	43,059	41,946
Costs and Expenses, Total	251,475	254,576	507,796	506,725
OPERATING INCOME	36,425	38,738	79,619	71,313
OTHER (INCOME) EXPENSE:
Interest expense, net	13,737	12,868	27,173	25,870
Other (income) expense	(123)	289	(152)	401
Total non-operating expense (income)	13,614	13,157	27,021	26,271
INCOME BEFORE INCOME TAXES	22,811	25,581	52,598	45,042
Income tax expense	(450)	(515)	(1,170)	(881)
INCOME BEFORE EQUITY IN SUBSIDIARIES	22,361	25,066	51,428	44,161
Income from equity in subsidiaries	23,114	32,517	44,094	59,729
NET INCOME	45,475	57,583	95,522	103,890
Reportable Legal Entities | Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES	361,548	386,740	726,298	764,217
EXPENSES:
Operating	299,659	308,480	606,906	615,150
General and administrative	17,946	18,532	34,436	35,818
Depreciation and amortization	15,089	21,290	29,998	42,458
Asset impairments			259
Costs and Expenses, Total	332,694	348,302	671,599	693,426
OPERATING INCOME	28,854	38,438	54,699	70,791
OTHER (INCOME) EXPENSE:
Interest expense, net	2,885	3,928	5,939	8,470
Other (income) expense	52	(153)	88	(344)
Total non-operating expense (income)	2,937	3,775	6,027	8,126
INCOME BEFORE INCOME TAXES	25,917	34,663	48,672	62,665
Income tax expense	(2,792)	(2,150)	(4,557)	(2,944)
INCOME BEFORE EQUITY IN SUBSIDIARIES	23,125	32,513	44,115	59,721
NET INCOME	23,125	32,513	44,115	59,721
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES	(213,055)	(216,723)	(431,636)	(431,539)
EXPENSES:
Operating	(213,055)	(216,723)	(431,636)	(431,539)
Costs and Expenses, Total	(213,055)	(216,723)	(431,636)	(431,539)
OTHER (INCOME) EXPENSE:
Other (income) expense	11	(4)	21	(8)
Total non-operating expense (income)	11	(4)	21	(8)
INCOME BEFORE INCOME TAXES	(11)	4	(21)	8
INCOME BEFORE EQUITY IN SUBSIDIARIES	(11)	4	(21)	8
Income from equity in subsidiaries	(23,114)	(32,517)	(44,094)	(59,729)
NET INCOME	$ (23,125)	$ (32,513)	$ (44,115)	$ (59,721)