Earnings Per Share (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified | 3 Months Ended | 9 Months Ended |
|---|
Sep. 30, 2011 | Sep. 30, 2010 | Sep. 30, 2011 | Sep. 30, 2010 |
|---|
| Numerator | | | | |
| Net income | $ 16,473 | $ 10,629 | $ 50,024 | $ 26,242 |
| Percentage allocated to shareholders (in hundredths) | 99.20% | 98.90% | 99.00% | 99.10% |
| Numerator for basic and diluted earnings per share | $ 16,341 | $ 10,512 | $ 49,524 | $ 26,005 |
| Denominator | | | | |
| Denominator for basic earnings per share - weighted-average shares outstanding (in shares) | 58,598 | 57,899 | 58,441 | 57,550 |
| Dilutive effect of stock options (in shares) | 389 | 583 | 445 | 676 |
| Dilutive effect of restricted stock units | | | 99 | |
| Denominator for diluted earnings per share (in shares) | 58,987 | 58,482 | 58,985 | 58,226 |
| Per share income | | | | |
| Basic (in dollars per share) | $ 0.28 | $ 0.18 | $ 0.85 | $ 0.45 |
| Diluted (in dollars per share) | $ 0.28 | $ 0.18 | $ 0.84 | $ 0.45 |
| Basic weighted-average shares outstanding (in shares) | 58,598 | 57,899 | 58,441 | 57,550 |
| Basic weighted-average shares outstanding and unvested restricted share units expected to vest (in shares) | 59,062 | 58,514 | 59,047 | 58,071 |
| Percentage allocated to shareholders (in hundredths) | 99.20% | 98.90% | 99.00% | 99.10% |