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Earnings (loss) per share (Details) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2016 | Jun. 30, 2015 | Jun. 30, 2016 | Jun. 30, 2015
Earnings Per Share [Abstract] |  |  |  |
Net income (loss) | $ (9,515) | $ (33,897) | $ (25,678) | $ 39,882
Amount allocated to common stockholders (in hundredths) | 100.00% | 100.00% | 100.00% | 91.84%
Basic EPS: |  |  |  |
Net income (loss) allocated to common stockholders | $ (9,515) | $ (33,897) | $ (25,678) | $ 36,628
Net income (loss) allocated to common stockholders - (shares) | 87,060,000 | 86,873,000 | 87,050,000 | 87,838,000
Net income (loss) allocated to common stockholders (in dollars per share) | $ (0.11) | $ (0.39) | $ (0.29) | $ 0.42
Effect of Dilutive Securities: |  |  |  |
Share-based compensation plans | $ 0 | $ 0 | $ 0 | $ 0
Share-based compensation plans - (shares) | 0 | 0 | 0 | 657,000
Diluted EPS: |  |  |  |
Net income (loss) allocated to common stockholders with assumed conversion | $ (9,515) | $ (33,897) | $ (25,678) | $ 36,628
Net income (loss) allocated to common stockholders with assumed conversion - (shares) | 87,060,000 | 86,873,000 | 87,050,000 | 88,495,000
Net income (loss) allocated to common stockholders with assumed conversion (in dollars per share) | $ (0.11) | $ (0.39) | $ (0.29) | $ 0.41
Stock options [Member] |  |  |  |
Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Securities excluded from calculation of diluted EPS (shares) | 372,902 | 543,171 | 277,617 | 332,766
Service-based share awards [Member] |  |  |  |
Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |
Securities excluded from calculation of diluted EPS (shares) | 1,427,194 | 691,773 | 1,010,856 | 0

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