Per Share Data (Calculation of Basic and Diluted EPS) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Earnings Per Share [Abstract]
Net income attributable to ISSI	$ 3,137	$ 8,090	$ 10,528	$ 21,083
Weighted average common shares outstanding (in shares)	27,316	26,768	27,002	26,546
Dilutive stock options and awards (in shares)	1,753	1,783	1,799	1,776
Denominator for diluted net income per share (in shares)	29,069	28,551	28,801	28,322
Basic net income per share (in dollars per share)	$ 0.11	$ 0.30	$ 0.39	$ 0.79
Diluted net income per share (in dollars per share)	$ 0.11	$ 0.28	$ 0.37	$ 0.74