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Summary of Significant Accounting Policies:Financial Instruments (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Reported Value Measurement [Member] | 5.625% Senior Notes Due 2024 [Member]    
Financial Instruments    
Fixed-rate debt $ 350.0 $ 350.0
Level 2 [Member] | Estimate of Fair Value Measurement [Member] | 5.625% Senior Notes Due 2024 [Member]    
Financial Instruments    
Fixed-rate debt 369.3 347.4
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Money Market Funds [Member]    
Financial Instruments    
Cash equivalents, fair value $ 137.5 $ 78.1