SELECTED QUARTERLY FINANCIAL DATA (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
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)
Net Revenues	$ 55,596	$ 57,109	$ 54,578	$ 49,749	$ 51,485	$ 53,576	$ 50,013	$ 47,171	$ 217,032	$ 202,245	$ 187,767
Operating expenses	45,404	44,857	45,633	42,590	43,498	43,527	41,965	40,700	178,484	169,690	165,548
Income from operations	10,192	12,252	8,945	7,159	7,987	10,049	8,048	6,471	38,548	32,555	22,219
Net income	$ 6,470	$ 7,834	$ 5,695	$ 4,575	$ 5,123	$ 6,394	$ 5,099	$ 4,043	$ 24,574	$ 20,659	$ 14,185
Income per share of common stock
Basic (in dollars per share)	$ 0.37	$ 0.45	$ 0.33	$ 0.27	$ 0.30	$ 0.38	$ 0.30	$ 0.24	$ 1.42	$ 1.22	$ 0.85
Diluted (in dollars per share)	$ 0.36	$ 0.45	$ 0.32	$ 0.26	$ 0.29	$ 0.37	$ 0.29	$ 0.24	$ 1.39	$ 1.19	$ 0.83