Inventory (Other Disclosures) (Details) (Natural Disasters and Other Casualty Events, USD $) In Millions, unless otherwise specified	9 Months Ended
Jun. 30, 2012
Natural Disasters and Other Casualty Events
Extraordinary Item [Line Items]
Inventory, damaged by Thailand flood, writedown (recovery)	$ 3.7

Inventory, Damaged from Thailand Flood, Writedown (Recovery)

No definition available.

Name:	emkr_InventoryDamagedFromThailandFloodWritedownRecovery
Namespace Prefix:	emkr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration