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Capital Stock (Details) - USD ($) $ / shares in Units, $ in Millions | 3 Months Ended | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019 | Dec. 31, 2019 | Sep. 12, 2020 | Jun. 11, 2019
Class of Stock [Line Items] |  |  |  |  |  |  |
Stock Repurchase Program, Number of Shares Authorized to be Repurchased |  |  |  |  |  | 5,500,000 |
Incremental Common Shares Attributable to Dilutive Effect of Accelerated Share Repurchase Agreements |  |  | 3,000,000.0 |  |  |  |
Stock repurchased and retired (in shares) | 1,445,300 | 4,200 | 2,539,041 | 43,560 |  |  |
Accelerated Share Repurchases, Adjustment to Recorded Amount | $ 46.3 |  | $ 77.5 |  |  |  |
Shares repurchased, average cost per share (in dollars per share) | $ 32.05 |  | $ 31.01 |  |  |  |
Shares repurchased during the period as percentage of shares authorized for repurchase (percent) | 26.30% |  | 45.50% |  |  |  |
Class A Common Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Shares outstanding (in shares) | 41,143,592 |  | 41,143,592 |  | 43,129,085 |  |
Stock Repurchase Program, Number of Shares Authorized to be Repurchased |  |  |  |  |  |  | 2,500,000
Stock repurchased and retired (in shares) | 1,445,300 |  | 2,500,000 |  | 0 |  |
Stock Repurchase Program, Remaining Number of Shares Authorized to be Repurchased | 3,000,000.0 |  | 3,000,000.0 |  |  |  |
Class B Common Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Shares outstanding (in shares) | 21,971,339 |  | 21,971,339 |  | 22,117,254 |  |
Director [Member] | Class A Common Stock |  |  |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |  |  |
Common Stock, Shares, Issued | 19,491 |  | 19,491 |  |  |  |
Dividend, Share-based Payment Arrangement, Paid-in-Kind |  |  | $ 0.6 |  |  |  |

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- Definition The adjustment needed to reconcile previously recorded amounts to the actual aggregate amount paid, whether in cash or other consideration, to acquire all of the shares purchased under an Accelerated Share Repurchase arrangement. + References No definition available. + Details
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