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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Earnings Per Share [Abstract]
Net income attributable to ISSI	$ 6,186	$ 7,064	$ 20,433	$ 12,850
Denominator for basic net income per share:
Weighted average common shares outstanding	30,312	28,293	29,816	27,988
Dilutive stock options and awards	1,651	1,462	1,521	1,439
Denominator for diluted net income per share	31,963	29,755	31,337	29,427
Basic net income per share (in dollars per share)	$ 0.20	$ 0.25	$ 0.69	$ 0.46
Diluted net income per share (in dollars per share)	$ 0.19	$ 0.24	$ 0.65	$ 0.44