SELECTED QUARTERLY FINANCIAL DATA (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
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)
Net Revenues	$ 56,056	$ 63,027	$ 58,229	$ 53,414	$ 55,596	$ 57,109	$ 54,578	$ 49,749	$ 230,726	$ 217,032	$ 202,245
Operating expenses	47,919	49,777	46,676	45,688	45,404	44,857	45,633	42,590	190,060	178,484	169,690
Income from operations	8,137	13,250	11,553	7,726	10,192	12,252	8,945	7,159	40,666	38,548	32,555
Net income	$ 4,397	$ 9,030	$ 7,239	$ 4,872	$ 6,470	$ 7,834	$ 5,695	$ 4,575	$ 25,538	$ 24,574	$ 20,659
Earnings per share of common stock
Basic (in dollars per share)	$ 0.25	$ 0.51	$ 0.41	$ 0.28	$ 0.37	$ 0.45	$ 0.33	$ 0.27	$ 1.45	$ 1.42	$ 1.22
Diluted (in dollars per share)	$ 0.23	$ 0.49	$ 0.40	$ 0.27	$ 0.36	$ 0.45	$ 0.32	$ 0.26	$ 1.39	$ 1.39	$ 1.19
Enactment of the Tax Cuts and Jobs Act in 2017
Negative effect on Net income from Deferred tax asset revaluation	$ 1,500								$ 1,461
Negative effect on Basic and Diluted EPS from Deferred tax asset revaluation (in dollars per share)	$ 0.08