Income per share data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Summary of reconciliation of the numerator and denominator of earnings per share computation
Net income	$ 2,356	$ 15,791	$ 4,057	$ 19,486
Weighted average basic common shares outstanding	27,550	26,670	27,392	26,189
Dilutive effect of stock-based awards	703	1,269	846	1,607
Weighted average diluted common shares outstanding	28,253	27,939	28,238	27,796
Earnings per share:
Basic	$ 0.09	$ 0.59	$ 0.15	$ 0.74
Diluted	$ 0.08	$ 0.57	$ 0.14	$ 0.70

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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+ Details

- Definition

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.

+ References+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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-Glossary Other Comprehensive Income

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-Glossary Net Income

-URI http://asc.fasb.org/extlink&oid=6518256

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+ Details

- Definition

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.

+ References+ Details

- Definition

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.

+ References

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-Glossary Weighted-Average Number of Common Shares Outstanding

-URI http://asc.fasb.org/extlink&oid=6528421

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