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Earnings (loss) per share (Details) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2015 | Jun. 30, 2014 | Jun. 30, 2015 | Jun. 30, 2014
Earnings Per Share [Abstract] |  |  |  |  |  |  |
Net income (loss) |  | $ (33,897) |  | $ 20,344 |  | $ 39,882 | $ 240
Amount allocated to common stockholders (in hundredths) |  | 100.00% | [1] | 91.80% | [1] | 91.84% | 91.78%
Basic EPS: |  |  |  |  |  |  |
Net income (loss) allocated to common stockholders |  | $ (33,897) |  | $ 18,675 |  | $ 36,628 | $ 220
Net income (loss) allocated to common stockholders - (in Shares) |  | 86,873,000 |  | 88,787,000 |  | 87,838,000 | 88,752,000
Net income (loss) allocated to common stockholders (in dollars per share) |  | $ (0.39) |  | $ 0.21 |  | $ 0.42 | $ 0.00
Effect of Dilutive Securities: |  |  |  |  |  |  |
Share-based compensation plans |  | $ 0 |  | $ 0 |  | $ 0 | $ 0
Share-based compensation plans - (in Shares) |  | 0 |  | 565,000 |  | 657,000 | 540,000
Diluted EPS: |  |  |  |  |  |  |
Net income (loss) allocated to common stockholders with assumed conversion |  | $ (33,897) |  | $ 18,675 |  | $ 36,628 | $ 220
Net income (loss) allocated to common stockholders with assumed conversion - (in Shares) |  | 86,873,000 |  | 89,352,000 |  | 88,495,000 | 89,292,000
Net income (loss) allocated to common stockholders with assumed conversion (in dollars per share) |  | $ (0.39) |  | $ 0.21 |  | $ 0.41 | $ 0.00
Stock options [Member] |  |  |  |  |  |  |
Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |  |  |  |
Securities excluded from calculation of diluted EPS (in shares) | [2] | 543,171 |  | 347,433 |  | 332,766 | 347,433
Service-based share awards [Member] |  |  |  |  |  |  |
Securities Excluded from Computation of Earnings Per Share [Line Items] |  |  |  |  |  |  |
Securities excluded from calculation of diluted EPS (in shares) | [2] | 691,773 |  | 0 |  | 0 | 0
[1] | We have not allocated net losses between common and preferred stockholders, as the holders of our preferred shares do not have a contractual obligation to share in the loss.
[2] | In periods when we report a net loss, all share awards are excluded from the calculation of diluted weighted average shares outstanding because of their antidilutive effect on earnings (loss) per share. In periods when we report net income, certain option awards may be excluded from the calculation of diluted EPS if the exercise price of the option award was greater than the average market price of the underlying common stock.

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