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Stock options and restricted common stock - Textual (Details) (USD $)
In Millions, except Per Share data, unless otherwise specified |
12 Months Ended | ||
|---|---|---|---|
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Dec. 31, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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| Disclosure of Compensation Related Costs, Share-based Payments [Abstract] | |||
| Contractual Term | 10 years | ||
| Weighted-average grant-date fair value of stock options granted | $ 8.31 | $ 4.10 | $ 3.41 |
| Aggregate intrinsic value of outstanding stock options | $ 16.3 | ||
| Compensation costs not yet recognized related to nonvested awards | $ 6.7 | ||
| Compensation costs not yet recognized related to nonvested awards, period for recognition | 3 years 10 days | ||