Stock Based Compensation Fair Value Assumptions for Stock Options (Details) (USD $)
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12 Months Ended | ||
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Dec. 31, 2012
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Dec. 31, 2011
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Dec. 31, 2010
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Two-Year Bonus Stock Options [Member]
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Risk-free interest rate | 2.29% | ||
Expected volatility | 45.70% | ||
Expected term (in years) | 4 years 6 months | ||
Weighted average grant date fair value of options granted during the period | $ 5.31 | ||
Five Year Service Stock Options [Member]
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Risk-free interest rate | 0.82% | 2.39% | 2.29% |
Expected volatility | 53.08% | 48.00% | 45.70% |
Expected term (in years) | 5 years 6 months | 5 years 6 months | 5 years 6 months |
Weighted average grant date fair value of options granted during the period | $ 5.85 | $ 6.58 | $ 5.84 |