Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]
Net sales	$ 328,977	$ 307,570	$ 265,950
Cost of sales	216,721	206,109	182,966
Gross profit	112,256	101,461	82,984
Operating expenses
Research and development	45,243	40,839	30,918
Selling, general and administrative	46,295	43,964	42,174
Impairment of goodwill	0	0	4,261
Total operating expenses	91,538	84,803	77,353
Operating income	20,718	16,658	5,631
Interest and other income (expense), net	1,236	1,247	(1,656)
Interest expense	(127)	(101)	(68)
Gain on sales of investments	11,300	12,217	0
Income before income taxes	33,127	30,021	3,907
Provision for income taxes	9,638	12,277	6,512
Consolidated net income (loss)	23,489	17,744	(2,605)
Less net income attributable to noncontrolling interests	(224)	(196)	(113)
Net income (loss) attributable to ISSI	$ 23,265	$ 17,548	$ (2,718)
Basic net income (loss) per share	$ 0.77	$ 0.62	$ (0.10)
Shares used in basic per share calculation	30,037	28,223	27,120
Diluted net income (loss) per share (in dollars per share)	$ 0.74	$ 0.59	$ (0.10)
Shares used in diluted per share calculation	31,623	29,694	27,120