QUARTERLY INFORMATION (UNAUDITED) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
QUARTERLY INFORMATION (UNAUDITED)
Revenues	$ 31,904	$ 31,361	$ 30,178	$ 28,354	$ 27,280	$ 26,018	$ 26,893	$ 23,180	$ 121,797	$ 103,371	$ 88,275
Gross profit	21,593	24,277	23,001	19,854	20,978	18,124	18,187	15,445	88,725	72,734
Net income (loss)	4,042	2,408	5,259	3,811	3,001	10,184	9,030	(576)	15,520	21,639	20,383
Net income (loss) applicable to common stockholders	$ 4,040	$ 2,405	$ 5,257	$ 3,808	$ 3,000	$ 10,181	$ 9,027	$ (579)	$ 15,510	$ 21,629	$ 20,365
Earnings (loss) per share
Basic (in dollars per share)	$ 0.06	$ 0.03	$ 0.07	$ 0.05	$ 0.04	$ 0.14	$ 0.13	$ (0.01)	$ 0.22	$ 0.31	$ 0.29
Diluted (in dollars per share)	$ 0.06	$ 0.03	$ 0.07	$ 0.05	$ 0.04	$ 0.14	$ 0.13	$ (0.01)	$ 0.22	$ 0.30	$ 0.29