Earnings per Share - Reconciliation of Weighted Average Number of Shares Outstanding (Details) - shares |
12 Months Ended | |
|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
|
| Earnings Per Share [Abstract] | ||
| Basic and diluted weighted average number of shares outstanding | 95,774,897 | 83,988,597 |
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||
| Anti-dilutive shares excluded from diluted weighted average number of shares outstanding (in shares) | 9,852,224 | 12,260,210 |
| Stock options | ||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||
| Anti-dilutive shares excluded from diluted weighted average number of shares outstanding (in shares) | 7,353,546 | 9,899,393 |
| Restricted share units | ||
| Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] | ||
| Anti-dilutive shares excluded from diluted weighted average number of shares outstanding (in shares) | 2,498,678 | 2,360,817 |