Inventories (Narrative) (Details) (VAC [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
VAC [Member]
Inventories [Line Items]
Remaining inventory step-up recognized as inventory on-hand	$ 8.3	$ 56.4

Remaining inventory step-up recognized as inventory on-hand.

No definition available.

Name:	omg_RemainingInventoryStepUpRecognizedAsInventoryOnHand
Namespace Prefix:	omg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant