Share-based compensation plans - Option Activity (Details)
|
9 Months Ended |
|
Sep. 30, 2018
$ / shares
shares
|
|---|
| Performance-Based Options |
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] |
|
| Beginning balance, shares | shares |
879,800
|
| Granted, shares | shares |
417,600
|
| Forfeited, shares | shares |
0
|
| Exercised, shares | shares |
0
|
| Ending balance, shares | shares |
1,297,400
|
| Weighted Average Grant Date Fair Value Per Share |
|
| Beginning balance (dollars per share) | $ / shares |
$ 8.04
|
| Granted (dollars per share) | $ / shares |
16.73
|
| Forfeited (dollars per share) | $ / shares |
0.00
|
| Exercised (dollars per share) | $ / shares |
0.00
|
| Ending balance (dollars per share) | $ / shares |
$ 10.83
|
| Time Based Vesting Option |
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] |
|
| Beginning balance, shares | shares |
40,600
|
| Granted, shares | shares |
0
|
| Forfeited, shares | shares |
0
|
| Exercised, shares | shares |
(37,900)
|
| Ending balance, shares | shares |
2,700
|
| Weighted Average Grant Date Fair Value Per Share |
|
| Beginning balance (dollars per share) | $ / shares |
$ 8.66
|
| Granted (dollars per share) | $ / shares |
0.00
|
| Forfeited (dollars per share) | $ / shares |
0.00
|
| Exercised (dollars per share) | $ / shares |
7.77
|
| Ending balance (dollars per share) | $ / shares |
$ 21.09
|