Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
REVENUES	$ 490,294		$ 449,929		$ 974,358	$ 890,845
EXPENSES:
Operating	345,679		320,539		691,511	639,690
General and administrative	33,364		27,538		62,809	52,509
Depreciation and amortization	35,591		38,560		71,114	76,649
Asset impairments	4,706		1,580		4,706	1,580
Costs and Expenses, Total	419,340		388,217		830,140	770,428
OPERATING INCOME	70,954		61,712		144,218	120,417
OTHER (INCOME) EXPENSE:
Interest expense, net	20,662		19,038		42,098	38,074
Expenses associated with debt refinancing transactions			1,016			1,016
Other (income) expense	(258)		33		(254)	(10)
Total non-operating expense (income)	20,404		20,087		41,844	39,080
INCOME BEFORE INCOME TAXES	50,550		41,625		102,374	81,337
Income tax expense	(1,972)		(2,428)		(4,456)	(4,363)
NET INCOME	$ 48,578	$ 49,340	$ 39,197	$ 37,777	$ 97,918	$ 76,974
BASIC EARNINGS PER SHARE	$ 0.41		$ 0.33		$ 0.82	$ 0.65
DILUTED EARNINGS PER SHARE	$ 0.41		$ 0.33		$ 0.82	$ 0.65