v2.4.1.9
DEBT (Narrative) (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Debt      
Long-term Line of Credit $ 0us-gaap_LineOfCredit   $ 0us-gaap_LineOfCredit
Line of Credit Facility, Current Borrowing Capacity 250,000,000us-gaap_LineOfCreditFacilityCurrentBorrowingCapacity    
Debt Instrument, Face Amount 150,000,000us-gaap_DebtInstrumentFaceAmount 150,000,000us-gaap_DebtInstrumentFaceAmount  
Proceeds from Notes Payable   149,300,000us-gaap_ProceedsFromDebtNetOfIssuanceCosts  
Interest Costs Incurred 1,700,000us-gaap_InterestCostsIncurred 1,700,000us-gaap_InterestCostsIncurred  
Capitalized Interest 0us-gaap_InterestCostsCapitalized 300,000us-gaap_InterestCostsCapitalized  
Series A Senior Notes      
Debt      
Debt Instrument, Face Amount 60,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriesaseniornotesMember
60,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriesaseniornotesMember
 
Debt Instrument, Interest Rate, Stated Percentage 3.23%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriesaseniornotesMember
3.23%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriesaseniornotesMember
 
Series B Senior Notes      
Debt      
Debt Instrument, Face Amount 45,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriesbseniornotesMember
45,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriesbseniornotesMember
 
Debt Instrument, Interest Rate, Stated Percentage 4.13%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriesbseniornotesMember
4.13%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriesbseniornotesMember
 
Series C Senior Notes      
Debt      
Debt Instrument, Face Amount 45,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriescseniornotesMember
45,000,000us-gaap_DebtInstrumentFaceAmount
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriescseniornotesMember
 
Debt Instrument, Interest Rate, Stated Percentage 4.28%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriescseniornotesMember
4.28%us-gaap_DebtInstrumentInterestRateStatedPercentage
/ us-gaap_LongtermDebtTypeAxis
= ipi_SeriescseniornotesMember
 
Unsecured credit facility      
Debt      
Line of Credit Facility, Maximum Borrowing Capacity 250,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= ipi_ExistingCreditFacilityMember
250,000,000us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
/ us-gaap_LineOfCreditFacilityAxis
= ipi_ExistingCreditFacilityMember
 
Maximum allowable leverage ratio 3.5    
Minimum allowable fixed charge coverage ratio 1.3    
Line of Credit Facility, Borrowings 0us-gaap_ProceedsFromLinesOfCredit
/ us-gaap_LineOfCreditFacilityAxis
= ipi_ExistingCreditFacilityMember
17,000,000us-gaap_ProceedsFromLinesOfCredit
/ us-gaap_LineOfCreditFacilityAxis
= ipi_ExistingCreditFacilityMember
 
Line of Credit Facility, Repayments $ 0us-gaap_RepaymentsOfLinesOfCredit
/ us-gaap_LineOfCreditFacilityAxis
= ipi_ExistingCreditFacilityMember
$ 17,000,000us-gaap_RepaymentsOfLinesOfCredit
/ us-gaap_LineOfCreditFacilityAxis
= ipi_ExistingCreditFacilityMember