Earnings per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Earnings per share
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	452,000
Calculation of basic and diluted earnings per share
Net income (loss)	$ (53,058)us-gaap_ProfitLoss	$ 65,607us-gaap_ProfitLoss
Basic weighted-average common shares outstanding	67,463,000	67,056,000
Add: dilutive effect of stock options, unvested RSU's, and contingent PSU's	0	1,070,000
Diluted weighted-average common shares outstanding	67,463,000	68,126,000
Basic net income (loss) per common share	$ (0.79)us-gaap_EarningsPerShareBasic	$ 0.98us-gaap_EarningsPerShareBasic
Diluted net income (loss) per common share	$ (0.79)us-gaap_EarningsPerShareDiluted	$ 0.96us-gaap_EarningsPerShareDiluted
Performance Shares [Member]
Earnings per share
Performance period to receive awards (in years)	3
Minimum PSU Multiplier [Member] \| Performance Shares [Member]
Earnings per share
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	0.00%
Maximum PSU Multiplier [Member] \| Performance Shares [Member]
Earnings per share
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage	200.00%

Period over which company performance is measured in order to compute the multiplier to apply to PSU awards

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Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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- Definition

Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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Percentage of vesting of share-based compensation awards.

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The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

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Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

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