Consolidated Statements of Comprehensive Income Statement (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Statement of Comprehensive Income [Abstract]
Consolidated net income (loss)	$ 17,744	$ (2,605)	$ 56,123
Change in unrealized gain (loss) on investments:
Changes arising during current year, net of tax benefit (expense) of $(7,975), $312 and $716 for fiscal 2013, 2012 and 2011, respectively	13,755	(1,523)	57
Reclassification for (gain) loss included in net income (loss), net of tax expense (benefit) of $3,823, $(716) and $0 for fiscal 2013, 2012 and 2011, respectively	(5,854)	1,213	0
Net change	7,901	(310)	57
Change in cumulative translation adjustment:
Changes arising during current year	(1,261)	3,932	1,850
Reclassification for gain included in net income (loss)	0	0	0
Translation adjustment, net change	(1,261)	3,932	1,850
Change in retirement plan transition obligation:
Changes arising during current year, net of tax benefit (expense) of $(44), $(119) and $0 for fiscal 2013, 2012 and 2011, respectively	(23)	(134)	10
Reclassification for gain included in net income (loss), net of tax expense (benefit) of $15 for fiscal 2013 and $0 for both fiscal 2012 and 2011	(45)	(62)	(60)
Transition obligation, net change	(68)	(196)	(50)
Change in retirement plan actuarial losses:
Changes arising during current year, net of tax benefit (expense) of $160, $323 and $0 for fiscal 2013, 2012 and 2011, respectively	63	127	(885)
Reclassification for gain included in net income (loss), net of tax expense (benefit) of $(13) for fiscal 2013 and $0 for both fiscal 2012 and 2011	87	98	62
Actuarial Losses, net change	150	225	(823)
Other comprehensive income	6,722	3,651	1,034
Comprehensive income	24,466	1,046	57,157
Comprehensive income attributable to noncontrolling interests	(196)	(113)	(166)
Comprehensive income attributable to ISSI	$ 24,270	$ 933	$ 56,991