SELECTED QUARTERLY INFORMATION (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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
Quarterly Financial Information Disclosure [Abstract]
Revenues		$ 114,457		$ 114,159	$ 102,865	$ 89,188	$ 93,307	$ 110,085	$ 109,482	$ 103,081	$ 420,669	$ 415,955	$ 431,755
Gross Profit		58,225		58,131	51,572	45,474	48,005	57,005	56,234	53,544	213,402	214,788	213,664
Net income (loss)		$ 158,291	[1]	$ 17,099	$ 10,845	$ 7,233	$ 22,736	$ 17,667	$ 15,381	$ 14,200	193,468	69,984	27,609
Litigation settlement											$ 168,969	$ 0	$ 0
Earnings per share
Basic		$ 5.38		$ 0.58	$ 0.37	$ 0.25	$ 0.78	$ 0.60	$ 0.52	$ 0.48	$ 6.61	$ 2.38	$ 0.93
Diluted	[2]	$ 5.28		$ 0.57	$ 0.37	$ 0.25	$ 0.77	$ 0.59	$ 0.51	$ 0.46	$ 6.49	$ 2.32	$ 0.90
Shares used in per share calculation
Basic		29,427		29,385	29,297	28,951	29,164	29,365	29,505	29,799	29,267	29,456	29,674
Diluted	[2]	30,005		29,866	29,702	29,446	29,651	29,998	30,183	30,552	29,816	30,147	30,545

[1] In October 2019 the Company entered into a favorable litigation settlement with ON Semiconductor Corporation which resulted in a $169.0 million net gain (Refer to Note 13, Legal Proceedings and Contingencies, in our Notes to Consolidated Financial Statements included in this Annual Report on Form 10-K).

[2] The Company includes the shares underlying performance-based awards in the calculation of diluted earnings per share if the performance conditions have been satisfied as of the end of the reporting period and excludes such shares when the necessary conditions have not been met. The Company has included in the 2019, 2018 and 2017 calculations those shares that were contingently issuable upon the satisfaction of the performance conditions as of the end of the respective periods.