SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)
Net Revenues	$ 62,080	$ 65,585	$ 62,761	$ 58,740	$ 59,779	$ 64,359	$ 59,909	$ 56,268	$ 249,166	$ 240,315	$ 230,726
Operating expenses	54,382	54,062	51,128	50,019	50,718	50,493	48,567	47,711	209,591	197,489	190,060
Income from operations	7,698	11,523	11,633	8,721	9,061	13,866	11,342	8,557	39,575	42,826	40,666
Net income	$ 6,196	$ 9,326	$ 9,279	$ 7,015	$ 7,259	$ 10,859	$ 9,239	$ 6,741	$ 31,816	$ 34,098	$ 25,538
Earnings per share of common stock
Basic (in dollars per share)	$ 0.34	$ 0.52	$ 0.52	$ 0.39	$ 0.40	$ 0.61	$ 0.52	$ 0.38	$ 1.77	$ 1.91	$ 1.45
Diluted (in dollars per share)	$ 0.33	$ 0.50	$ 0.50	$ 0.38	$ 0.39	$ 0.58	$ 0.50	$ 0.36	$ 1.70	$ 1.83	$ 1.39