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Financial Instruments	12 Months Ended
Financial Instruments	Dec. 31, 2017
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Instruments and Hedging Activities Disclosure	Financial Instruments We are exposed to capital market risk, such as changes in interest rates. In an effort to manage interest rate risk, we may enter into interest rate hedging arrangements from time to time. We do not utilize derivative financial instruments for trading or speculative purposes. The effectiveness of our hedges is evaluated throughout their lives using the hypothetical derivative method under which the change in fair value of the actual swap designated as the hedging instrument is compared to the change in fair value of a hypothetical swap. We had no material interest rate derivatives, when considering the fair value of the hedging instruments, in any period presented.