v2.4.1.9
COMPENSATION PLANS (Narrative) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding non-vested equity-based awards, end of period (in shares) 481,288us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
  464,769us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
Period over which grants vest (in years) 3 years    
Allocated Share-based Compensation Expense $ 0.9us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
$ 0.8us-gaap_AllocatedShareBasedCompensationExpense
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
 
Total unrecognized compensation expense $ 6.8us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockMember
   
Performance Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding non-vested equity-based awards, end of period (in shares) 383,447us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardTypeAxis
= ipi_PerformanceUnitsMember
   
Period over which grants vest (in years) 3 years    
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding non-qualified stock options, end of period (in shares) 319,972us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
   
Period over which grants vest (in years) 3 years    
Common Stock Awards      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Common stock available for issuance under the Plan (in shares) 2,900,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_AwardTypeAxis
= ipi_CommonStockAwardsMember
   
Restricted Stock Awards, Granted To Newly Hired Employees | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Period over which grants vest (in years) 1 year    
Restricted Stock Awards, Granted To Newly Hired Employees | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Period over which grants vest (in years) 4 years    
2015 Performance Units [Member] | Performance Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding non-vested equity-based awards, end of period (in shares) 378,150us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardDateAxis
= ipi_A2015PerformanceUnitsMember
/ us-gaap_AwardTypeAxis
= ipi_PerformanceUnitsMember
   
2012-2013 Performance [Member] | Performance Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Outstanding non-vested equity-based awards, end of period (in shares) 5,297us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
/ us-gaap_AwardDateAxis
= ipi_A20122013PerformanceMember
/ us-gaap_AwardTypeAxis
= ipi_PerformanceUnitsMember