QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ 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
Revenue	$ 100,841	$ 94,558	$ 94,290	$ 94,713	$ 78,341	$ 69,804	$ 55,136	$ 50,935	$ 384,402	$ 254,216	$ 167,350
Operating income (loss)	13,402	14,150	12,715	11,845	8,248	7,773	6,775	5,718	52,112	28,514	(969)
Income (loss) from continuing operations	8,021	7,280	9,002	6,905	32,081	7,383	6,439	5,413	31,208	51,316	(487)
Income (loss) from discontinued operations	(697)	(664)	(1,150)	(1,203)	(31)	(1,295)	(1,717)	(226)	(3,714)	(3,269)	9,849
Net income (loss) and comprehensive income (loss)	$ 7,324	$ 6,616	$ 7,852	$ 5,702	$ 32,050	$ 6,088	$ 4,722	$ 5,187	$ 27,494	$ 48,047	$ 9,362
Basic (in dollars per share)	$ 0.68	$ 0.62	$ 0.76	$ 0.58	$ 2.69	$ 0.65	$ 0.57	$ 0.48	$ 2.64	$ 4.46	$ (0.04)
Diluted (in dollars per share)	0.63	0.57	0.71	0.54	2.47	0.59	0.52	0.44	2.44	4.09	(0.04)
Income (loss) per share from discontinued operations:
Basic (in dollars per share)	(0.06)	(0.06)	(0.10)	(0.10)	0.00	(0.11)	(0.15)	(0.02)
Diluted (in dollars per share)	(0.05)	(0.05)	(0.09)	(0.09)	0.00	(0.10)	(0.14)	(0.02)
Income (loss) per share from continuing operations:
Basic (in dollars per share)	0.62	0.56	0.67	0.48	2.69	0.53	0.41	0.46	2.33	4.17	0.84
Diluted (in dollars per share)	$ 0.57	$ 0.52	$ 0.62	$ 0.44	$ 2.47	$ 0.49	$ 0.38	$ 0.43	$ 2.15	$ 3.83	$ 0.84