QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
QUARTERLY RESULTS OF OPERATIONS (UNAUDITED)
Revenues	$ 664,848	$ 711,295	$ 658,646	$ 577,904	$ 578,549	$ 623,414	$ 576,899	$ 520,687	$ 2,612,693	$ 2,299,549	$ 2,065,999
Operating expenses	646,799	678,354	631,694	586,606	565,047	602,912	568,482	544,037	2,543,454	2,280,479	2,080,567
OPERATING INCOME (LOSS)	18,049	32,941	26,952	(8,702)	13,502	20,502	8,417	(23,350)	69,239	19,070	(14,568)
Other income (costs), net	1,591	(385)	419	(253)	393	502	(552)	47	1,373	391	(2,424)
Income tax provision (benefit)	5,097	12,938	10,163	(3,762)	3,549	7,022	2,987	(9,908)	24,435	3,650	(9,260)
Net income (loss)	$ 14,543	$ 19,618	$ 17,208	$ (5,193)	$ 10,346	$ 13,982	$ 4,878	$ (13,395)	$ 46,177	$ 15,811	$ (7,732)
Earnings (loss) per common share
Basic (in dollars per share)	$ 0.53	$ 0.72	$ 0.63	$ (0.20)	$ 0.38	$ 0.52	$ 0.18	$ (0.52)	$ 1.69	$ 0.59	$ (0.31)
Diluted (in dollars per share)	$ 0.53	$ 0.72	$ 0.63	$ (0.20)	$ 0.38	$ 0.52	$ 0.18	$ (0.52)	$ 1.69	$ 0.59	$ (0.31)
AVERAGE COMMON SHARES OUTSTANDING
Basic (in shares)	26,073,256	26,054,678	26,005,105	25,876,928	25,785,485	25,736,810	25,694,327	25,638,333	25,993,255	25,714,205	25,564,752
Diluted (in shares)	26,073,256	26,054,678	26,005,105	25,876,928	25,793,366	25,736,810	25,694,327	25,638,333	25,993,612	25,714,205	25,564,752