Stock incentive plan (Details) - USD ($)
|
12 Months Ended |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] |
|
|
|
| Options outstanding, beginning of period (in shares) |
2,929
|
6,830
|
6,210
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross |
0
|
0
|
884
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period |
(592)
|
(3,901)
|
(264)
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period |
0
|
0
|
0
|
| Options outstanding, end of period (in shares) |
2,337
|
2,929
|
6,830
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number |
2,337
|
1,730
|
5,318
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract] |
|
|
|
| Options outstanding, beginning of period (in dollars per share) |
$ 24.47
|
$ 92.34
|
$ 99.03
|
| Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price |
0
|
0
|
25.28
|
| Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price |
25.48
|
168.79
|
25.28
|
| Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price |
0
|
0
|
0
|
| Options outstanding, end of period (in dollars per share) |
24.21
|
24.47
|
92.34
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract] |
|
|
|
| Options outstanding, beginning of the period, fair value (in dollars per share) |
12.71
|
57.97
|
64.96
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value |
0
|
0
|
15.52
|
| Share Based Compensation Arrangement By Share Based Payment Award Options Forfeited Fair Value |
12.53
|
95.85
|
80.33
|
| Share Based Compensation Arrangement By Share Based Payment Award Options Exercised During Period Fair Value |
0
|
0
|
0
|
| Options outstanding, ending balance fair value (in dollars per share) |
$ 12.76
|
$ 12.71
|
$ 57.97
|
| Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value |
$ 0
|
$ 0
|
$ 0
|