Quarterly Financial Information (Details) (USD $)	3 Months Ended												12 Months Ended
	Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Schedule of Quarterly Financial Information [Line Items]
Gain (Loss) on Sale of Equity Investments			$ 7,300,000
Net sales	78,392,000		77,788,000		74,991,000		76,399,000	72,500,000		64,781,000	62,505,000	66,164,000	307,570,000	265,950,000	270,508,000
Gross profit	25,934,000		26,047,000		24,989,000		24,491,000	18,328,000	[1]	21,337,000	21,121,000	22,198,000	101,461,000	82,984,000	90,408,000
Operating income	4,693,000		4,635,000		3,951,000		3,379,000	(9,862,000)	[2]	5,196,000	5,197,000	5,100,000	16,658,000	5,631,000	26,169,000
Consolidated net income (loss)	4,730,000	[3]	7,246,000	[4]	3,280,000	[5]	2,488,000	(13,118,000)	[6]	3,147,000	3,597,000	3,769,000	17,744,000	(2,605,000)	56,123,000
Net income attributable to ISSI	4,698,000	[3]	7,064,000	[4]	3,287,000	[5]	2,499,000	(13,246,000)	[6]	3,137,000	3,601,000	3,790,000	17,548,000	(2,718,000)	55,957,000
Basic net income per share (in dollars per share)	$ 0.16		$ 0.25		$ 0.12		$ 0.09	$ (0.48)		$ 0.11	$ 0.13	$ 0.14	$ 0.62	$ (0.10)	$ 2.11
Diluted net income (loss) per share (in dollars per share)	$ 0.15		$ 0.24		$ 0.11		$ 0.09	$ (0.48)		$ 0.11	$ 0.12	$ 0.13	$ 0.59	$ (0.10)	$ 1.98
Market price range common stock:
Impairment of intangible assets													0	8,887,000	145,000
Write-down of investment								2,300,000
Maximum
Market price range common stock:
Share Price	$ 11.99		$ 11.31		$ 9.92		$ 9.73	$ 10.49		$ 11.50	$ 11.40	$ 9.79	$ 11.99	$ 10.49
Minimum
Market price range common stock:
Share Price	$ 9.99		$ 8.31		$ 8.33		$ 8.18	$ 8.75		$ 8.83	$ 9.03	$ 6.81	$ 9.99	$ 8.75
SMIC
Market price range common stock:
Write-down of investment								2,300,000
Si En
Market price range common stock:
Impairment of intangible assets								5,400,000
Impairment of tangible and intangible assets								14,300,000
Nanya
Schedule of Quarterly Financial Information [Line Items]
Gain (Loss) on Sale of Equity Investments	$ 2,900,000		$ 7,000,000		$ 2,100,000

[1] In the September 2012 quarter, the Company recorded a charge of approximately $5.4 million for the impairment of certain intangible assets related to the acquisition of Si En.

[2] In the September 2012 quarter, the Company recorded a charge of approximately $14.3 million for the impairment of certain tangible and intangible assets related to the acquisition of Si En.

[3] In the September 2013 quarter, the Company realized a gain of $2.9 million from the sale of a portion of its Nanya shares.

[4] In the June 2013 quarter, the Company realized a gain from the sale of investments of $7.3 million including $7.0 million from the sale of a portion of its Nanya shares.

[5] In the March 2013 quarter, the Company realized a gain of $2.1 million from the sale of a portion of its Nanya shares.

[6] In the September 2012 quarter, the Company recorded a charge of approximately $14.3 million for the impairment of certain tangible and intangible assets related to the acquisition of Si En and a charge of approximately $2.3 million to write-down its investment in SMIC due to the decline in fair market value being considered other than temporary.