Quarterly Financial Information (Details) (USD $)	3 Months Ended										12 Months Ended
	Sep. 30, 2012		Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011		Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Schedule of Quarterly Financial Information [Line Items]
Net sales	$ 72,500,000		$ 64,781,000	$ 62,505,000	$ 66,164,000	$ 71,339,000		$ 69,809,000	$ 63,257,000	$ 66,103,000	$ 265,950,000	$ 270,508,000	$ 252,458,000
Gross profit	18,328,000	[1]	21,337,000	21,121,000	22,198,000	23,838,000		23,170,000	20,935,000	22,465,000	82,984,000	90,408,000	96,531,000
Operating income	(9,862,000)	[2]	5,196,000	5,197,000	5,100,000	6,794,000		7,525,000	5,502,000	6,348,000	5,631,000	26,169,000	39,956,000
Consolidated net income (loss)	(13,118,000)	[3]	3,147,000	3,597,000	3,769,000	35,056,000	[4]	8,095,000	5,758,000	7,214,000	(2,605,000)	56,123,000	42,755,000
Net income (loss) attributable to ISSI	(13,246,000)	[3]	3,137,000	3,601,000	3,790,000	34,874,000	[4]	8,090,000	5,781,000	7,212,000	(2,718,000)	55,957,000	42,196,000
Basic net income (loss) per share (in dollars per share)	$ (0.48)		$ 0.11	$ 0.13	$ 0.14	$ 1.31		$ 0.30	$ 0.22	$ 0.27	$ (0.10)	$ 2.11	$ 1.65
Diluted net income (loss) per share (in dollars per share)	$ (0.48)		$ 0.11	$ 0.12	$ 0.13	$ 1.23		$ 0.28	$ 0.20	$ 0.26	$ (0.10)	$ 1.98	$ 1.56
Market price range common stock:
Impairment of intangible assets											8,887,000	145,000	0
Write-down of investment	2,300,000
Income tax benefit from release of valuation allowance for certain deferred tax assets						28,100,000					1,384,000	(28,136,000)	0
Maximum
Market price range common stock:
Share Price	$ 10.49		$ 11.50	$ 11.40	$ 9.79	$ 9.84		$ 10.17	$ 11.79	$ 9.50	$ 10.49	$ 9.84
Minimum
Market price range common stock:
Share Price	$ 8.75		$ 8.83	$ 9.03	$ 6.81	$ 7.49		$ 8.45	$ 8.08	$ 7.01	$ 8.75	$ 7.49
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

[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 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.

[4] In the September 2011 quarter, the Company recorded an income tax benefit of approximately $28.1 million from the release of the valuation allowance for certain deferred tax assets.