SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED)
Net Revenues	$ 59,779	$ 64,359	$ 59,909	$ 56,268	$ 56,056	$ 63,027	$ 58,229	$ 53,414	$ 240,315	$ 230,726	$ 217,032
Operating expenses	50,718	50,493	48,567	47,711	47,919	49,777	46,676	45,688	197,489	190,060	178,484
Income from operations	9,061	13,866	11,342	8,557	8,137	13,250	11,553	7,726	42,826	40,666	38,548
Net income	$ 7,259	$ 10,859	$ 9,239	$ 6,741	$ 4,397	$ 9,030	$ 7,239	$ 4,872	$ 34,098	$ 25,538	$ 24,574
Earnings per share of common stock
Basic (in dollars per share)	$ 0.40	$ 0.61	$ 0.52	$ 0.38	$ 0.25	$ 0.51	$ 0.41	$ 0.28	$ 1.91	$ 1.45	$ 1.42
Diluted (in dollars per share)	$ 0.39	$ 0.58	$ 0.50	$ 0.36	$ 0.23	$ 0.49	$ 0.40	$ 0.27	$ 1.83	$ 1.39	$ 1.39
Enactment of the Tax Cuts and Jobs Act in 2017
Negative effect on Net income from Deferred tax asset revaluation					$ 1,500
Negative effect on Basic and Diluted EPS from Deferred tax asset revaluation (in dollars per share)					$ 0.08