Per Share Data (Calculation of Basic and Diluted EPS) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share [Abstract]
Net income attributable to ISSI	$ 5,435	$ 2,499
Denominator for basic net income per share:
Weighted average common shares outstanding	29,318	27,696
Dilutive stock options and awards	1,399	1,410
Denominator for diluted net income per share	30,717	29,106
Basic net income per share (in dollars per share)	$ 0.19	$ 0.09
Diluted net income per share (in dollars per share)	$ 0.18	$ 0.09