QUARTERLY RESULTS OF OPERATIONS (UNAUDITED) (Details) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares	Jun. 30, 2016 USD ($) $ / shares shares	Mar. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares
QUARTERLY RESULTS OF OPERATIONS (UNAUDITED)
Revenues	$ 688,214	$ 713,923	$ 676,627	$ 621,455	$ 648,134	$ 709,380	$ 696,115	$ 613,276	$ 2,700,219	$ 2,666,905	$ 2,612,693
Operating expenses	687,003	693,553	659,973	630,720	640,822	675,942	662,649	611,996	2,671,249	2,591,409	2,543,454
OPERATING INCOME	1,211	20,370	16,654	(9,265)	7,312	33,438	33,466	1,280	28,970	75,496	69,239
Other income (costs), net	(115)	185	(273)	(480)	(445)	(1,392)	(557)	(368)	(683)	(2,762)	1,373
Income tax provision (benefit)	(488)	7,615	6,150	(3,642)	1,878	12,892	12,942	167	9,635	27,880	24,435
NET INCOME	$ 1,584	$ 12,940	$ 10,231	$ (6,103)	$ 4,989	$ 19,154	$ 19,967	$ 745	$ 18,652	$ 44,854	$ 46,177
Earnings (loss) per common share
Basic (in dollars per share) | $ / shares	$ 0.06	$ 0.50	$ 0.39	$ (0.24)	$ 0.19	$ 0.73	$ 0.76	$ 0.03	$ 0.72	$ 1.71	$ 1.69
Diluted (in dollars per share) | $ / shares	$ 0.06	$ 0.49	$ 0.39	$ (0.24)	$ 0.19	$ 0.72	$ 0.74	$ 0.03	$ 0.71	$ 1.67	$ 1.69
AVERAGE COMMON SHARES OUTSTANDING
Basic (in shares) | shares	25,669,280	25,724,550	25,791,026	25,822,522	25,936,709	26,009,344	26,021,874	26,051,038	25,751,544	26,013,716	25,993,255
Diluted (in shares) | shares	26,272,487	26,211,524	26,246,868	25,822,522	26,415,839	26,508,482	26,593,451	26,588,518	26,256,570	26,530,127	25,993,612
Restructuring charges
Restructuring charges	$ 10,300								$ 10,313
Restructuring charges, after-tax	$ 6,300
Impact of restructuring charges on earnings per share (in dollars per share) | $ / shares	(0.24)