Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 445,684	$ 447,385
EXPENSES:
Operating	315,303	313,918
General and administrative	24,826	26,480
Depreciation and amortization	36,257	42,059
Asset impairments	259
Costs and Expenses, Total	376,645	382,457
Operating income	69,039	64,928
OTHER (INCOME) EXPENSE:
Interest expense, net	16,490	17,544
Other (income) expense	17	(83)
Total non-operating expense (income)	16,507	17,461
INCOME BEFORE INCOME TAXES	52,532	47,467
Income tax expense	(2,485)	(1,160)
INCOME BEFORE EQUITY IN SUBSIDIARIES	50,047	46,307
NET INCOME	50,047	46,307
Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES	299,515	284,724
EXPENSES:
Operating	226,637	222,064
General and administrative	8,336	9,194
Depreciation and amortization	21,348	20,891
Costs and Expenses, Total	256,321	252,149
Operating income	43,194	32,575
OTHER (INCOME) EXPENSE:
Interest expense, net	13,436	13,002
Other (income) expense	(29)	112
Total non-operating expense (income)	13,407	13,114
INCOME BEFORE INCOME TAXES	29,787	19,461
Income tax expense	(720)	(366)
INCOME BEFORE EQUITY IN SUBSIDIARIES	29,067	19,095
Income from equity in subsidiaries	20,980	27,212
NET INCOME	50,047	46,307
Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES	364,750	377,477
EXPENSES:
Operating	307,247	306,670
General and administrative	16,490	17,286
Depreciation and amortization	14,909	21,168
Asset impairments	259
Costs and Expenses, Total	338,905	345,124
Operating income	25,845	32,353
OTHER (INCOME) EXPENSE:
Interest expense, net	3,054	4,542
Other (income) expense	36	(191)
Total non-operating expense (income)	3,090	4,351
INCOME BEFORE INCOME TAXES	22,755	28,002
Income tax expense	(1,765)	(794)
INCOME BEFORE EQUITY IN SUBSIDIARIES	20,990	27,208
NET INCOME	20,990	27,208
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES	(218,581)	(214,816)
EXPENSES:
Operating	(218,581)	(214,816)
Costs and Expenses, Total	(218,581)	(214,816)
OTHER (INCOME) EXPENSE:
Other (income) expense	10	(4)
Total non-operating expense (income)	10	(4)
INCOME BEFORE INCOME TAXES	(10)	4
INCOME BEFORE EQUITY IN SUBSIDIARIES	(10)	4
Income from equity in subsidiaries	(20,980)	(27,212)
NET INCOME	$ (20,990)	$ (27,208)