Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
REVENUES	$ 508,522			$ 462,728			$ 1,482,880	$ 1,353,573
EXPENSES:
Operating	368,735			333,759			1,060,246	973,449
General and administrative	32,038			25,085			94,847	77,594
Depreciation and amortization	36,654			39,465			107,768	116,114
Asset impairments							4,706	1,580
Costs and Expenses, Total	437,427			398,309			1,267,567	1,168,737
OPERATING INCOME	71,095			64,419			215,313	184,836
OTHER (INCOME) EXPENSE:
Interest expense, net	20,975			20,534			63,073	58,608
Expenses associated with debt refinancing transactions								1,016
Other (income) expense	(360)			49			(614)	39
Total non-operating expense (income)	20,615			20,583			62,459	59,663
INCOME BEFORE INCOME TAXES	50,480			43,836			152,854	125,173
Income tax expense	(1,486)			(2,842)			(5,942)	(7,205)
NET INCOME	$ 48,994	$ 48,578	$ 49,340	$ 40,994	$ 39,197	$ 37,777	$ 146,912	$ 117,968
BASIC EARNINGS PER SHARE	$ 0.41			$ 0.35			$ 1.23	$ 1.00
DILUTED EARNINGS PER SHARE	$ 0.41			$ 0.34			$ 1.23	$ 0.99