CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Senior Subordinated Convertible Debenture Due 2025 [Member]	Junior Subordinated Convertible Debentures Due2037 Member	Supertex Inc. [Member]	Common Stock and Additional Paid-in Capital	Common Stock and Additional Paid-in Capital Supertex Inc. [Member]	Common Stock and Additional Paid-in Capital Micrel Incorporated [Member]	Common Stock Held in Treasury	Accumulated Other Comprehensive Income (Loss)	Retained Earnings	Parent [Member]	Parent [Member] Senior Subordinated Convertible Debenture Due 2025 [Member]	Parent [Member] Junior Subordinated Convertible Debentures Due2037 Member	Parent [Member] Supertex Inc. [Member]	Noncontrolling Interest [Member]
Balance at Mar. 31, 2013	$ 1,933,470				$ 1,255,823			$ (682,220)	$ 6,935	$ 1,352,932	$ 1,933,470				$ 0
Balance, common stock shares issued (in shares) at Mar. 31, 2013					218,790,000
Balance, common stock held in treasury (in shares) at Mar. 31, 2013								22,317,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	395,281									395,281	395,281
Other comprehensive income (loss)	(5,884)								(5,884)		(5,884)
Proceeds from sales of common stock through employee equity incentive plans (shares)					4,161,000
Proceeds from sales of common stock through employee equity incentive plans (amount)	60,086				$ 60,086						60,086
Restricted stock unit and stock appreciation right withholdings (shares)					(631,000)
Restricted stock unit and stock appreciation right withholdings (amount)	(22,640)				$ (22,640)						(22,640)
Treasury stock used for new issuances (shares)					(3,530,000)			(3,530,000)
Treasury stock used for new issuances (amount)					$ (104,838)			$ 104,838
Tax benefit (shortfall) from equity incentive plans	1,411				1,411						1,411
Share-based compensation	54,941				54,941						54,941
Cash dividend	(281,204)									(281,204)	(281,204)
Balance at Mar. 31, 2014	2,135,461				$ 1,244,783			$ (577,382)	1,051	1,467,009	2,135,461				0
Balance, common stock shares issued (in shares) at Mar. 31, 2014					218,790,000
Balance, common stock held in treasury (in shares) at Mar. 31, 2014								18,787,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Additions due to acquisition of controlling interest in ISSC	52,467														52,467
Net income	365,325									369,009	369,009				(3,684)
Other comprehensive income (loss)	9,750								10,616		10,616				(866)
Other	240														240
Purchase of additional interests	(32,095)				$ 345				(591)		(246)				(31,849)
Proceeds from sales of common stock through employee equity incentive plans (shares)					2,503,000
Proceeds from sales of common stock through employee equity incentive plans (amount)	34,433				$ 34,369						34,369				64
Restricted stock unit and stock appreciation right withholdings (shares)					(426,000)
Restricted stock unit and stock appreciation right withholdings (amount)	(19,504)				$ (19,504)						(19,504)
Treasury stock used for new issuances (shares)					(2,077,000)			(2,077,000)
Treasury stock used for new issuances (amount)					$ (61,703)			$ 61,703
Tax benefit (shortfall) from equity incentive plans	1,220				1,220						1,220
Share-based compensation	56,687				56,687						56,687
Non-cash consideration, exchange of employee stock awards (amount)				$ 1,622		$ 1,622								$ 1,622
Convertible Debt - retirement of 2037 debentures			$ (606,926)		(606,926)								$ (606,926)
Convertible Debt - issuance of 2025 debentures		$ 348,824			348,824							$ 348,824
Cash dividend	(286,478)									(286,478)	(286,478)
Balance at Mar. 31, 2015	$ 2,061,026				$ 999,717			$ (515,679)	11,076	1,549,540	2,044,654				16,372
Balance, common stock shares issued (in shares) at Mar. 31, 2015	218,789,994				218,790,000
Balance, common stock held in treasury (in shares) at Mar. 31, 2015	16,709,688							16,710,000
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 323,925									324,132	324,132				(207)
Other comprehensive income (loss)	(14,158)								(14,158)		(14,158)				0
Purchase of additional interests	(18,051)				$ (1,611)				(275)		(1,886)				(16,165)
Proceeds from sales of common stock through employee equity incentive plans (shares)					2,491,000
Proceeds from sales of common stock through employee equity incentive plans (amount)	28,718				$ 28,718						28,718				0
Restricted stock unit and stock appreciation right withholdings (shares)					(489,000)
Restricted stock unit and stock appreciation right withholdings (amount)	(21,720)				$ (21,720)						(21,720)
Treasury stock used for new issuances (shares)					(2,002,000)			(2,002,000)
Treasury stock used for new issuances (amount)					$ (59,442)			$ 59,442
Tax benefit (shortfall) from equity incentive plans	(567)				(567)						(567)
Share-based compensation	73,556				73,556						73,556
Issuance of common stock - acquisitions (shares)							8,627,000
Issuance of common stock - acquisitions (amount)	369,054						$ 369,054				369,054
Non-cash consideration, exchange of employee stock awards (amount)	$ 4,052						$ 4,052				4,052
Purchase of treasury stock (shares)	8,600,000							8,627,000
Purchase of treasury stock (amount)	$ (363,829)							$ (363,829)			(363,829)
Cash dividend	(291,087)									(291,087)	(291,087)
Balance at Mar. 31, 2016	$ 2,150,919				$ 1,391,757			$ (820,066)	$ (3,357)	$ 1,582,585	$ 2,150,919				$ 0
Balance, common stock shares issued (in shares) at Mar. 31, 2016	227,416,789				227,417,000
Balance, common stock held in treasury (in shares) at Mar. 31, 2016	23,335,062							23,335,000