Summary of Significant Accounting Policies:Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Reported Value Measurement [Member] | 4.875% Senior Notes Due 2030 [Member]
Financial Instruments [Line Items]
Fixed-rate debt	$ 400.0
Reported Value Measurement [Member] | 5.625% Senior Notes Due 2024 [Member]
Financial Instruments [Line Items]
Fixed-rate debt		$ 350.0
Level 2 [Member] | Estimate of Fair Value Measurement [Member] | 4.875% Senior Notes Due 2030 [Member]
Financial Instruments [Line Items]
Fixed-rate debt	432.0
Level 2 [Member] | Estimate of Fair Value Measurement [Member] | 5.625% Senior Notes Due 2024 [Member]
Financial Instruments [Line Items]
Fixed-rate debt		364.7
Money Market Funds [Member] | Fair Value, Recurring [Member] | Level 1 [Member]
Financial Instruments [Line Items]
Cash equivalents, fair value	$ 371.8	$ 259.5