Shareholders' Equity - Additional Information (Details) |
12 Months Ended |
|---|---|
|
Dec. 31, 2017
vote
| |
| Class A Subordinate Voting | |
| Class of Stock [Line Items] | |
| Voting rights (in votes per share) | 1 |
| Class B Multiple Voting | |
| Class of Stock [Line Items] | |
| Voting rights (in votes per share) | 10 |
| Voting shares convertible (per share) | 1 |