RETIREMENT PLAN AND POST-RETIREMENT BENEFITS, Plan Changes (Details) (USD $) In Thousands, unless otherwise specified						12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2011 Supplemental Executive Retirement and Restoration Plans [Member]	Dec. 31, 2011 Contract with IBEW No. 1245 Amendment [Member] Pension Benefits [Member]	Dec. 31, 2011 MPAT Amendment [Member] Other Post-Retirement Benefits [Member]	Dec. 31, 2011 Amendment to Cap Company Contributions [Member] Other Post-Retirement Benefits [Member]	Dec. 31, 2011 Amendment to Cap Company Contributions [Member] Supplemental Executive Retirement and Restoration Plans [Member]
Defined Benefit Plan Amendments [Line Items]
Plan changes, description						Effective December 2010, under the terms of SPPC’s new contract with IBEW No. 1245, as ratified in August 2010, the pension plan for most bargaining unit employees was changed from a traditional defined benefit pension plan to a defined benefit cash balance pension plan. Employees with combined age and service totaling 75 years or more were given the choice of staying with the current pension plan or switch to the new cash balance pension plan. This plan amendment, as indicated in the benefits obligations table below, reduced the 2010 projected benefit obligation for pension plans by $10.4 million.	Additionally during 2010, benefits available to retired MPAT employees for health insurance coverage were amended. Retirees were given a choice between Health Reimbursement Accounts (HRA’s) and Health Savings Accounts (HSA’s). This plan amendment, as indicated in the benefits obligations table below, reduced the 2010 other postretirement benefit obligation by $0.7 million.	During 2009, in an effort to reduce costs, NVE implemented severance programs, as discussed in Note 17, Severance Programs. Under the terms of the program employees close to retirement age were offered special enhancements to bridge their pension and postretirement benefits. NVE recognized expense of $0.3 million for pension benefits and $2.8 million for other postretirement benefits in 2009, under the special termination provisions of the Compensation Nonretirement Postemployment Benefits Topic of the FASC.	NVE also has a non-qualified Supplemental Executive Retirement Plan and a Restoration Plan for executives. NVE contributed $26.5 million to establish a rabbi trust for these plans in 2009. Assets held in the trust for these non-contributory defined benefit plans consist of a variety of marketable securities and life insurance policies, none of which is NVE stock. At December 31, 2011 trust assets were $29.2 million and are reflected in NVE’s consolidated balance sheet within “Investments and other property, net”. NVE’s obligation under these supplemental and restoration plans is included in “Accrued retirement benefits” in NVE’s consolidated balance sheet, and amounted to $29.3 million at December 31, 2011. NVE is not required to make contributions to the plans.
Trust assets	$ 29,182	[1]	$ 29,348	[1]	$ 29,200

[1] Amounts recognized as non-current liabilities (accrued retirement benefits) in the consolidated balance sheets as of December 31, 2011 and 2010.