Fair Value Measurements (Marketable Equity and Cash Equivalents (Classified as Available-for-sale) and Cost Method Investments) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended	12 Months Ended
	Mar. 31, 2014	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 35,935	$ 43,112
Gross Unrealized Holding Gains	1,616	10,218
Gross Unrealized Holding Losses	0	0
Fair Value	37,551	53,330
Money market instruments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19,320	19,318
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair Value	19,320	19,318
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	15,154	15,595
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair Value	15,154	15,595
Cash and Cash Equivalents
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,513	31,772
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Fair Value	32,513	31,772
Short-term Investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,422	11,340
Gross Unrealized Holding Gains	1,616	10,218
Gross Unrealized Holding Losses	0	0
Fair Value	5,038	21,558
Semiconductor Manufacturing International Corp. | Available-for-sale Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,099
Gross Unrealized Holding Gains		694
Gross Unrealized Holding Losses		0
Fair Value		1,793
Nanya Technology Corporation | Available-for-sale Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,461	7,100
Gross Unrealized Holding Gains	1,616	9,524
Gross Unrealized Holding Losses	0	0
Fair Value	$ 3,077	$ 16,624