Equity (Narrative) (Details)	Dec. 31, 2019 plan
Equity [Abstract]
Number of equity incentive compensation plans maintained by the company	4

Number of equity incentive compensation plans maintained by the Company.

No definition available.

Name:	emkr_NumberOfEquityIncentiveCompensationPlans
Namespace Prefix:	emkr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant