QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
QUARTERLY RESULTS OF OPERATIONS (UNAUDITED)
Revenues	$ 648,134	$ 709,380	$ 696,115	$ 613,276	$ 664,848	$ 711,295	$ 658,646	$ 577,904	$ 2,666,905	$ 2,612,693	$ 2,299,549
Operating expenses	640,822	675,942	662,649	611,996	646,799	678,354	631,694	586,606	2,591,409	2,543,454	2,280,479
OPERATING INCOME	7,312	33,438	33,466	1,280	18,049	32,941	26,952	(8,702)	75,496	69,239	19,070
Other income (costs), net	(445)	(1,392)	(557)	(368)	1,591	(385)	419	(253)	(2,762)	1,373	391
Income tax provision (benefit)	1,878	12,892	12,942	167	5,097	12,938	10,163	(3,762)	27,880	24,435	3,650
NET INCOME	$ 4,989	$ 19,154	$ 19,967	$ 745	$ 14,543	$ 19,618	$ 17,208	$ (5,193)	$ 44,854	$ 46,177	$ 15,811
Earnings (loss) per common share
Basic (in dollars per share)	$ 0.19	$ 0.73	$ 0.76	$ 0.03	$ 0.53	$ 0.72	$ 0.63	$ (0.20)	$ 1.71	$ 1.69	$ 0.59
Diluted (in dollars per share)	$ 0.19	$ 0.72	$ 0.74	$ 0.03	$ 0.53	$ 0.72	$ 0.63	$ (0.20)	$ 1.67	$ 1.69	$ 0.59
AVERAGE COMMON SHARES OUTSTANDING
Basic (in shares)	25,936,709	26,009,344	26,021,874	26,051,038	26,073,256	26,054,678	26,005,105	25,876,928	26,013,716	25,993,255	25,714,205
Diluted (in shares)	26,415,839	26,508,482	26,593,451	26,588,518	26,073,256	26,054,678	26,005,105	25,876,928	26,530,127	25,993,612	25,714,205