Stock Incentive Plans - Aggregate Intrinsic Value of Awards Vested and Exercised (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of shares vested and exercised	$ 5.8	$ 5.5	$ 3.8
Performance shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of shares vested and exercised	$ 2.4	$ 1.6	$ 1.2

Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Exercises in Period, Total Intrinsic Value

No definition available.

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Namespace Prefix:	core_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration