Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Income Statement [Abstract]
Net sales	$ 307,570	$ 265,950	$ 270,508
Cost of sales	206,109	182,966	180,100
Gross profit	101,461	82,984	90,408
Operating expenses
Research and development	40,839	30,918	27,622
Selling, general and administrative	43,964	42,174	36,617
Impairment of goodwill	0	4,261	0
Total operating expenses	84,803	77,353	64,239
Operating income	16,658	5,631	26,169
Interest and other income (expense), net	1,247	(1,656)	2,144
Interest expense	(101)	(68)	(88)
Gain on sales of investments, net	12,217	0	560
Income before income taxes	30,021	3,907	28,785
Provision (benefit) for income taxes	12,277	6,512	(27,338)
Consolidated net income (loss)	17,744	(2,605)	56,123
Less net income attributable to noncontrolling interests	(196)	(113)	(166)
Net income (loss) attributable to ISSI	$ 17,548	$ (2,718)	$ 55,957
Basic net income (loss) per share (in dollars per share)	$ 0.62	$ (0.10)	$ 2.11
Shares used in basic per share calculation	28,223	27,120	26,568
Diluted net income (loss) per share (in dollars per share)	$ 0.59	$ (0.10)	$ 1.98
Shares used in diluted per share calculation	29,694	27,120	28,308