SELECTED QUARTERLY INFORMATION - 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
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Total revenue, net	$ 255,664	$ 250,332	$ 249,309	$ 236,770	$ 241,160	$ 226,367	$ 212,673	$ 202,534	$ 992,075	$ 882,734	$ 796,717
Gross margin	170,242	161,003	159,744	151,997	151,159	140,298	137,422	127,313	642,986	556,192
Continuing Operations, Net (loss) income	$ 28,246	$ 20,144	$ 12,755	$ 13,419	$ 14,980	$ (31,881)	$ 12,020	$ 11,732	$ 74,564	$ 6,851	$ 36,295
Continuing Operations, Per Share-Basic (in dollars per share)	$ 0.38	$ 0.27	$ 0.17	$ 0.18	$ 0.20	$ (0.45)	$ 0.18	$ 0.18	$ 1.00	$ 0.10	$ 0.56
Continuing Operations, Per Share-Diluted (in dollars per share)	$ 0.35	$ 0.25	$ 0.16	$ 0.18	$ 0.20	$ (0.45)	$ 0.18	$ 0.18	$ 0.94	$ 0.10	$ 0.55
Net income (loss)	$ 28,246	$ 20,144	$ 12,755	$ 13,419	$ 14,980	$ (31,881)	$ 4,998	$ 8,384	$ 74,564	$ (3,519)	$ 34,004
Net Income, Per Share-Basic (in dollars per share)	$ 0.38	$ 0.27	$ 0.17	$ 0.18	$ 0.20	$ (0.45)	$ 0.08	$ 0.13	$ 1.00	$ (0.05)	$ 0.52
Net Income, Per Share-Diluted (in dollars per share)	$ 0.35	$ 0.25	$ 0.16	$ 0.18	$ 0.20	$ (0.45)	$ 0.08	$ 0.13	$ 0.94	$ (0.05)	$ 0.52
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income, restated to reflect the effect of adoption				$ 1,800