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
CONSOLIDATED STATEMENTS OF OPERATIONS
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)
Interest and dividend income									1,523	1,284	851
Interest and other related financing costs									(5,150)	(4,400)	(3,190)
Other, net									2,944	354	3,712
TOTAL OTHER INCOME (COSTS)	(115)	185	(273)	(480)	(445)	(1,392)	(557)	(368)	(683)	(2,762)	1,373
INCOME BEFORE INCOME TAXES									28,287	72,734	70,612
INCOME TAX PROVISION	(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 PER COMMON SHARE
Basic (in dollars per share)	$ 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)	$ 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)	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)	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
CASH DIVIDENDS DECLARED PER COMMON SHARE (in dollars per share)	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.08	$ 0.06	$ 0.06	$ 0.06	$ 0.32	$ 0.26	$ 0.15