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Common Shareholders' Equity (Details) |  | 1 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jan. 01, 2017 shares | Nov. 30, 2009 shares | Dec. 31, 2018 vote shares | Dec. 31, 2017 shares | Dec. 31, 2016 shares
Series A Common Shares |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Number of votes | vote |  |  | 10 |  |
Voting rights for number of board of directors |  |  | 75% |  |
Common Shares |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Number of votes | vote |  |  | 1 |  |
Voting rights for number of board of directors |  |  | 25% |  |
Common Shares | 401(k) |  |  |  |  |
Share repurchases |  |  |  |  |
Shares reserved (in shares) |  |  | 67,000 |  |
Common Shares | Treasury shares |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Repurchase authorization, cumulative shares authorized (in shares) |  |  | 5,901,000 |  |
Common shareholders' equity, other disclosures |  |  |  |  |
Shares reissued (in shares) |  |  | 1,000,000 | 0 | 1,000,000
Common Shares | Treasury shares | Minimum |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Repurchase authorization, additional number of shares per year (in shares) | 0 |  |  |  |
Common Shares | Treasury shares | Maximum |  |  |  |  |
Class of Stock [Line Items] |  |  |  |  |
Repurchase authorization, additional number of shares per year (in shares) | 1,300,000 | 1,300,000 |  |  |

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