Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 447,385	$ 426,000
EXPENSES:
Operating	313,918	300,662
General and administrative	26,480	26,872
Depreciation and amortization	42,059	28,685
Asset impairments		955
Costs and Expenses	382,457	357,174
OPERATING INCOME	64,928	68,826
OTHER (INCOME) EXPENSE:
Interest expense, net	17,544	10,190
Other (income) expense	(83)	(26)
Total non-operating expense (income)	17,461	10,164
INCOME BEFORE INCOME TAXES	47,467	58,662
Income tax expense	(1,160)	(1,385)
INCOME BEFORE EQUITY IN SUBSIDIARIES	46,307	57,277
NET INCOME	46,307	57,277
Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES	284,724	303,040
EXPENSES:
Operating	222,064	221,677
General and administrative	9,194	8,800
Depreciation and amortization	20,891	20,069
Costs and Expenses	252,149	250,546
OPERATING INCOME	32,575	52,494
OTHER (INCOME) EXPENSE:
Interest expense, net	13,002	8,427
Other (income) expense	112	171
Total non-operating expense (income)	13,114	8,598
INCOME BEFORE INCOME TAXES	19,461	43,896
Income tax expense	(366)	(176)
INCOME BEFORE EQUITY IN SUBSIDIARIES	19,095	43,720
Income from equity in subsidiaries	27,212	13,557
NET INCOME	46,307	57,277
Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES	377,477	335,223
EXPENSES:
Operating	306,670	291,248
General and administrative	17,286	18,072
Depreciation and amortization	21,168	8,616
Asset impairments		955
Costs and Expenses	345,124	318,891
OPERATING INCOME	32,353	16,332
OTHER (INCOME) EXPENSE:
Interest expense, net	4,542	1,763
Other (income) expense	(191)	(121)
Total non-operating expense (income)	4,351	1,642
INCOME BEFORE INCOME TAXES	28,002	14,690
Income tax expense	(794)	(1,209)
INCOME BEFORE EQUITY IN SUBSIDIARIES	27,208	13,481
NET INCOME	27,208	13,481
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES	(214,816)	(212,263)
EXPENSES:
Operating	(214,816)	(212,263)
Costs and Expenses	(214,816)	(212,263)
OTHER (INCOME) EXPENSE:
Other (income) expense	(4)	(76)
Total non-operating expense (income)	(4)	(76)
INCOME BEFORE INCOME TAXES	4	76
INCOME BEFORE EQUITY IN SUBSIDIARIES	4	76
Income from equity in subsidiaries	(27,212)	(13,557)
NET INCOME	$ (27,208)	$ (13,481)