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Incentive Stock Plans - Performance Share Units - Narrative (Details) (Performance Shares [Member], USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Performance Shares [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Award vesting period 3 years
Valuation method Monte Carlo simulation model
Unrecognized compensation cost $ 1.6us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Weighted average period for recognition 2 years 0 months 0 days
Risk-free rate, description The risk-free rate was based on the 3-year U.S. treasury rate on the date of the award.
Dividend yield, description The dividend yield was not used to calculate fair value as all awards granted after January 1, 2010 receive dividend equivalents.