Business Acquisitions (Schedule of Purchase Price Allocation) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended	6 Months Ended
	Mar. 31, 2015	Mar. 31, 2015	Mar. 31, 2014	Jun. 30, 2014	Sep. 30, 2014	Aug. 01, 2012
Business Acquisition [Line Items]
Goodwill	$ 571,271	$ 571,271	$ 276,097
Supertex Inc. [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	14,790	14,790		14,790
Short-term investments	140,984	140,984		140,984
Accounts receivable, net	7,047	7,047		7,047
Inventories	27,630	27,630		27,630
Prepaid expenses	1,493	1,493		1,493
Deferred tax assets	2,456	2,456		3,997
Other current assets	12,625	12,625		16,113
Property, plant and equipment, net	15,679	15,679		15,679
Goodwill	143,160	143,160		133,713
Purchased intangible assets	89,600	89,600		89,600
Other assets	325	325		325
Total assets acquired	455,789	455,789		451,371
Accounts payable	(8,481)	(8,481)		(8,481)
Other current liabilities	(19,224)	(19,224)		(19,345)
Long-term income tax payable	(3,796)	(3,796)		(3,796)
Deferred tax liability	(32,511)	(32,511)		(27,972)
Total liabilities assumed	(64,012)	(64,012)		(59,594)
Net assets acquired	391,777	391,777		391,777
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract]
Deferred tax assets	(1,541)
Other current assets	(3,488)
Goodwill	9,447
Total assets acquired	4,418
Accrued liabilities	121
Deferred tax liability	(4,539)
Total liabilities assumed	(4,418)
ISSC Technologies Corporation [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	15,120	15,120			15,120
Short-term investments	27,063	27,063			27,063
Accounts receivable, net	8,792	8,792			8,792
Inventories	16,542	16,542			19,160
Prepaid expenses and other current assets	2,501	2,501			2,501
Property, plant and equipment, net	2,637	2,637			2,637
Goodwill	154,399	154,399			152,243
Purchased intangible assets	147,800	147,800			147,800
Other assets	1,370	1,370			1,370
Total assets acquired	376,224	376,224			376,686
Accounts payable	(9,860)	(9,860)			(9,860)
Other current liabilities	(16,535)	(16,535)			(16,997)
Long-term income tax payable	(4,402)	(4,402)			(4,402)
Deferred tax liability	(25,126)	(25,126)			(25,126)
Other long-term liabilities	(245)	(245)			(245)
Total liabilities assumed	(56,168)	(56,168)			(56,630)
Net assets acquired	320,056	320,056			320,056
Less: noncontrolling interest	(52,467)	(52,467)			(52,467)
Net assets acquired	267,589	267,589			267,589
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustments [Abstract]
Inventories		(2,618)
Goodwill		2,156
Total assets acquired		(462)
Accrued liabilities		462
Total liabilities assumed		462
SMSC Acquisition [Member]
Business Acquisition [Line Items]
Cash and cash equivalents						180,925
Accounts receivable, net						58,441
Inventories						86,244
Prepaid expenses						5,617
Deferred tax assets						15,843
Other current assets						17,578
Property, plant and equipment, net						35,608
Long-term investments						24,275
Goodwill						165,592
Intangible assets, net						10,214
Purchased intangible assets						517,800
Other assets						3,835
Total assets acquired						1,121,972
Accounts payable						(28,035)
Other current liabilities						(62,247)
Deferred income on shipments to distributors						(11,376)
Long-term income tax payable						(72,781)
Deferred tax liability						(16,682)
Other long-term liabilities						(11,250)
Total liabilities assumed						(202,371)
Net assets acquired						$ 919,601