EARNINGS PER SHARE (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
Basic earnings per share:
Net income		$ 158,291	[1]	$ 17,099	$ 10,845	$ 7,233	$ 22,736	$ 17,667	$ 15,381	$ 14,200	$ 193,468	$ 69,984	$ 27,609
Weighted-average common shares		29,427,000		29,385,000	29,297,000	28,951,000	29,164,000	29,365,000	29,505,000	29,799,000	29,267,000	29,456,000	29,674,000
Basic earnings per share		$ 5.38		$ 0.58	$ 0.37	$ 0.25	$ 0.78	$ 0.60	$ 0.52	$ 0.48	$ 6.61	$ 2.38	$ 0.93
Diluted earnings per share:
Net income		$ 158,291	[1]	$ 17,099	$ 10,845	$ 7,233	$ 22,736	$ 17,667	$ 15,381	$ 14,200	$ 193,468	$ 69,984	$ 27,609
Weighted-average common shares		29,427,000		29,385,000	29,297,000	28,951,000	29,164,000	29,365,000	29,505,000	29,799,000	29,267,000	29,456,000	29,674,000
Effect of dilutive securities:
Employee stock plans	[2]										549,000	691,000	871,000
Diluted weighted average common shares	[2]	30,005,000		29,866,000	29,702,000	29,446,000	29,651,000	29,998,000	30,183,000	30,552,000	29,816,000	30,147,000	30,545,000
Diluted earnings per share	[2]	$ 5.28		$ 0.57	$ 0.37	$ 0.25	$ 0.77	$ 0.59	$ 0.51	$ 0.46	$ 6.49	$ 2.32	$ 0.90
Antidilutive shares attributable to stock-based awards outstanding excluded from computation of diluted earnings per share											0	0	0

[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.