Per Share Data (Calculation of Basic and Diluted EPS) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2013	Mar. 31, 2012
Earnings Per Share [Abstract]
Net income attributable to ISSI	$ 3,287	$ 3,601	$ 5,786	$ 7,391
Denominator for basic net income per share:
Weighted average common shares outstanding	27,976	27,053	27,836	26,845
Dilutive stock options and awards	1,372	1,860	1,404	1,797
Denominator for diluted net income per share	29,348	28,913	29,240	28,642
Basic net income per share (in dollars per share)	$ 0.12	$ 0.13	$ 0.21	$ 0.28
Diluted net income per share (in dollars per share)	$ 0.11	$ 0.12	$ 0.20	$ 0.26