Share-based compensation plans - Stock activity - DSUs (Details)
|
1 Months Ended |
9 Months Ended |
12 Months Ended |
|
Jan. 31, 2016
director
$ / shares
shares
|
Sep. 30, 2016
$ / shares
shares
|
Dec. 31, 2015
$ / shares
shares
|
| Deferred Stock Units |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Vesting period (in years) |
|
|
1 year
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] |
|
|
|
| Nonvested, beginning balance, shares | shares |
21,400
|
21,400
|
|
| Granted, shares | shares |
|
29,700
|
|
| Forfeited, shares | shares |
|
0
|
|
| Vested, shares | shares |
|
(21,400)
|
|
| Nonvested, ending balance, shares | shares |
|
29,700
|
21,400
|
| Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] |
|
|
|
| Nonvested, beginning balance (dollars per share) | $ / shares |
$ 32.79
|
$ 32.79
|
|
| Granted (dollars per share) | $ / shares |
|
29.41
|
|
| Forfeited (dollars per share) | $ / shares |
|
0.00
|
|
| Vested (dollars per share) | $ / shares |
|
31.72
|
|
| Nonvested, ending balance (dollars per share) | $ / shares |
|
$ 29.41
|
$ 32.79
|
| Director | Severance Costs | Executive Leadership and Board of Directors Restructuring |
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
| Number of directors retired | director |
2
|
|
|