Inventory (Other Disclosures) (Details) (Natural Disasters and Other Casualty Events, USD $) In Millions, unless otherwise specified	12 Months Ended
Sep. 30, 2012
Natural Disasters and Other Casualty Events
Extraordinary Item [Line Items]
Inventory, damaged by Thailand flood, loss (recovery)	$ 3.7

Inventory, Damaged from Thailand Flood Loss (Recovery)

No definition available.

Name:	emkr_InventoryDamagedfromThailandFloodLossRecovery
Namespace Prefix:	emkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration