Condensed Consolidating Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Condensed Financial Statements, Captions [Line Items]
REVENUES	$ 459,957	$ 408,474	$ 1,345,252	$ 1,223,390
EXPENSES:
Operating	326,500	282,712	945,197	857,702
General and administrative	26,791	27,635	76,770	79,586
Depreciation and amortization	41,230	28,277	108,315	85,413
Asset impairments			955	2,238
Costs and Expenses	394,521	338,624	1,131,237	1,024,939
OPERATING INCOME	65,436	69,850	214,015	198,451
OTHER (INCOME) EXPENSE:
Interest expense (income), net	11,764	10,376	33,715	29,088
Expenses associated with debt refinancing transactions	701		701
Other (income) expense	(363)	(143)	(353)	(1,143)
Total non-operating expense (income)	12,102	10,233	34,063	27,945
INCOME BEFORE INCOME TAXES	53,334	59,617	179,952	170,506
Income tax expense	(2,658)	(2,071)	(6,696)	(5,490)
INCOME BEFORE EQUITY IN SUBSIDIARIES	50,676	57,546	173,256	165,016
NET INCOME	50,676	57,546	173,256	165,016
Parent
Condensed Financial Statements, Captions [Line Items]
REVENUES	294,578	319,127	899,992	939,686
EXPENSES:
Operating	226,020	226,820	669,653	671,914
General and administrative	8,226	8,719	23,725	25,648
Depreciation and amortization	20,623	20,389	60,967	60,266
Asset impairments				2,238
Costs and Expenses	254,869	255,928	754,345	760,066
OPERATING INCOME	39,709	63,199	145,647	179,620
OTHER (INCOME) EXPENSE:
Interest expense (income), net	7,739	8,821	24,420	26,232
Expenses associated with debt refinancing transactions	701		701
Other (income) expense	131	250	91	87
Total non-operating expense (income)	8,571	9,071	25,212	26,319
INCOME BEFORE INCOME TAXES	31,138	54,128	120,435	153,301
Income tax expense	(480)	(208)	(1,001)	(342)
INCOME BEFORE EQUITY IN SUBSIDIARIES	30,658	53,920	119,434	152,959
Income from equity in subsidiaries	20,018	3,626	53,822	12,057
NET INCOME	50,676	57,546	173,256	165,016
Combined Subsidiary Guarantors
Condensed Financial Statements, Captions [Line Items]
REVENUES	384,840	310,597	1,093,011	936,352
EXPENSES:
Operating	319,941	277,142	923,295	838,436
General and administrative	18,565	18,916	53,045	53,938
Depreciation and amortization	20,607	7,888	47,348	25,147
Asset impairments			955
Costs and Expenses	359,113	303,946	1,024,643	917,521
OPERATING INCOME	25,727	6,651	68,368	18,831
OTHER (INCOME) EXPENSE:
Interest expense (income), net	4,025	1,555	9,295	2,856
Other (income) expense	(469)	(61)	(479)	(589)
Total non-operating expense (income)	3,556	1,494	8,816	2,267
INCOME BEFORE INCOME TAXES	22,171	5,157	59,552	16,564
Income tax expense	(2,178)	(1,863)	(5,695)	(5,148)
INCOME BEFORE EQUITY IN SUBSIDIARIES	19,993	3,294	53,857	11,416
NET INCOME	19,993	3,294	53,857	11,416
Consolidating Adjustments and Other
Condensed Financial Statements, Captions [Line Items]
REVENUES	(219,461)	(221,250)	(647,751)	(652,648)
EXPENSES:
Operating	(219,461)	(221,250)	(647,751)	(652,648)
Costs and Expenses	(219,461)	(221,250)	(647,751)	(652,648)
OTHER (INCOME) EXPENSE:
Other (income) expense	(25)	(332)	35	(641)
Total non-operating expense (income)	(25)	(332)	35	(641)
INCOME BEFORE INCOME TAXES	25	332	(35)	641
INCOME BEFORE EQUITY IN SUBSIDIARIES	25	332	(35)	641
Income from equity in subsidiaries	(20,018)	(3,626)	(53,822)	(12,057)
NET INCOME	$ (19,993)	$ (3,294)	$ (53,857)	$ (11,416)