QUARTERLY SUPPLEMENTARY FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Continuing Operations [Abstract]
Total revenues	$ 273,355	$ 269,617	$ 258,487	$ 251,278	$ 264,537	$ 255,625	$ 244,866	$ 231,334	$ 1,052,737	$ 996,362	$ 899,271
Income (loss) before income taxes	29,369	(32,394)	(4,331)	23,006	13,925	14,035	1,372	28,165	15,650	57,497	115,370
Net income (loss)	$ 45,259	$ (19,082)	$ 109	$ 18,584	$ 12,035	$ 11,628	$ 3,435	$ 22,020	$ 44,870	$ 49,118	$ 85,320
Basic earnings per share (in dollars per share)	$ 1.81	$ (0.77)	$ 0.00	$ 0.73	$ 0.46	$ 0.46	$ 0.13	$ 0.87	$ 1.79	$ 1.94	$ 3.41
Diluted earnings per share (in dollars per share)	$ 1.78	$ (0.77)	$ 0.00	$ 0.72	$ 0.46	$ 0.45	$ 0.13	$ 0.86	$ 1.75	$ 1.90	$ 3.38
Discontinued Operations [Abstract]
Total revenues	$ 28,386	$ 27,054	$ 28,492	$ 31,781	$ 37,458	$ 33,869	$ 34,907	$ 34,351	$ 115,713	$ 140,585
Income before income taxes	2,294	1,880	4,386	2,083	(71)	1,140	(508)	609	10,643	1,170
Net income	$ 734	$ 1,218	$ 2,849	$ 1,352	$ (40)	$ 740	$ (321)	$ 407	$ 6,153	$ 786	$ 3,806
Basic earnings per share (in dollars per share)	$ 0.03	$ 0.05	$ 0.11	$ 0.05	$ 0.00	$ 0.03	$ (0.01)	$ 0.02	$ 0.24	$ 0.03	$ 0.15
Diluted earnings per share (in dollars per share)	$ 0.03	$ 0.05	$ 0.11	$ 0.05	$ 0.00	$ 0.03	$ (0.01)	$ 0.02	$ 0.24	$ 0.03	$ 0.15