Consolidated Statements of Operations - Entity [Domain] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
REVENUES:	$ 459,295	$ 410,694	$ 885,295	$ 814,916
EXPENSES:
Operating	318,035	287,610	618,697	574,990
General and administrative	23,107	26,559	49,979	51,951
Depreciation and amortization	38,400	28,752	67,085	57,136
Asset impairments		2,238	955	2,238
Costs and Expenses, Total	379,542	345,159	736,716	686,315
OPERATING INCOME	79,753	65,535	148,579	128,601
OTHER (INCOME) EXPENSE:
Interest expense, net	11,761	8,364	21,951	18,712
Other (income) expense	36	(613)	10	(1,000)
Total non-operating expense (income)	11,797	7,751	21,961	17,712
INCOME BEFORE INCOME TAXES	67,956	57,784	126,618	110,889
Income tax expense	(2,653)	(2,052)	(4,038)	(3,419)
NET INCOME	$ 65,303	$ 55,732	$ 122,580	$ 107,470
BASIC EARNINGS PER SHARE	$ 0.56	$ 0.48	$ 1.05	$ 0.93
DILUTED EARNINGS PER SHARE	0.55	0.48	1.04	0.92
Dividend declared on common stock, per share	$ 0.54	$ 0.51	$ 1.08	$ 1.02