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Note 1 - Summary of Significant Accounting Policies (Details) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]    
Long-term Line of Credit $ 50,200,000us-gaap_LineOfCredit  
Asset Impairment Charges 0us-gaap_AssetImpairmentCharges 0us-gaap_AssetImpairmentCharges
Environmental Remediation Expense 142,000us-gaap_EnvironmentalRemediationExpense 165,000us-gaap_EnvironmentalRemediationExpense
Minimum [Member]    
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]    
Debt Instrument, Covenant Required Liquidity 3,000,000mlp_DebtInstrumentCovenantRequiredLiquidity
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
 
Property, Plant and Equipment, Useful Life 3 years  
Maximum [Member]    
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]    
Debt Instrument, Covenant Required Liquidity $ 175,000,000mlp_DebtInstrumentCovenantRequiredLiquidity
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
 
Property, Plant and Equipment, Useful Life 40 years