Stockholders' Equity (Schedule of Comprehensive Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Stockholders' Equity Note [Abstract]
Consolidated net income	$ 3,147	$ 8,095	$ 10,513	$ 21,067
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Change in cumulative translation adjustment	(1,176)	1,757	1,872	6,516
Change in unrealized gains (losses) on investments	(314)	(139)	(324)	11
Change in retirement plan actuarial losses	24	15	71	45
Change in retirement plan transition obligation	(16)	(15)	(45)	(44)
Comprehensive income	1,665	9,713	12,087	27,595
Comprehensive (income) loss attributable to noncontrolling interest	(10)	(5)	15	16
Comprehensive income attributable to ISSI	$ 1,655	$ 9,708	$ 12,102	$ 27,611

The change in equity [net assets] of a business enterprise during a period from transactions and other events and circumstances from non-owner sources which are attributable to the reporting entity. It includes all changes in equity during a period except those resulting from investments by owners and distributions to owners, but excludes any and all transactions which are directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent.

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Net of tax amount of unrealized holding gain (loss) before reclassification adjustments and transfers on available-for-sale securities.

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