Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
REVENUES	$ 464,134	$ 474,935	$ 463,331	$ 447,385	$ 447,835	$ 459,957	$ 459,295	$ 426,000	$ 1,849,785	$ 1,793,087	$ 1,646,867
EXPENSES:
Operating									1,275,586	1,256,128	1,156,135
General and administrative									107,027	103,936	106,429
Depreciation and amortization									166,746	151,514	113,925
Restructuring charges									4,010	0	0
Asset impairments										955	30,082
Costs and Expenses, Total									1,553,369	1,512,533	1,406,571
OPERATING INCOME	80,359	73,953	77,176	64,928	66,539	65,436	79,753	68,826	296,416	280,554	240,296
OTHER (INCOME) EXPENSE:
Interest expense, net									67,755	49,696	39,535
Expenses associated with debt refinancing transactions									0	701	0
Other (income) expense									489	(58)	(1,204)
Total non-operating expense (income)									68,244	50,339	38,331
INCOME BEFORE INCOME TAXES									228,172	230,215	201,965
Income tax expense									(8,253)	(8,361)	(6,943)
NET INCOME	$ 60,689	$ 55,340	$ 57,583	$ 46,307	$ 48,598	$ 50,676	$ 65,303	$ 57,277	$ 219,919	$ 221,854	$ 195,022
BASIC EARNINGS PER SHARE	$ 0.52	$ 0.47	$ 0.49	$ 0.39	$ 0.41	$ 0.43	$ 0.56	$ 0.49	$ 1.87	$ 1.90	$ 1.68
DILUTED EARNINGS PER SHARE	$ 0.52	$ 0.47	$ 0.49	$ 0.39	$ 0.41	$ 0.43	$ 0.55	$ 0.49	1.87	1.88	1.66
DIVIDENDS DECLARED PER SHARE									$ 2.04	$ 2.16	$ 2.04