|
401(k) savings plan (Details) (USD $)
In Millions, unless otherwise specified |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2013
|
Dec. 31, 2012
|
Dec. 31, 2011
|
|
| 401(k) savings plan [Abstract] | |||
| Matching of qualified deferrals by employer, maximum (in hundredths) | 50.00% | ||
| Percentage of employee's gross salary subject to employer's matching contribution (in hundredths) | 6.00% | ||
| Matching contributions made by employer | $ 2.0 | $ 1.9 | $ 1.8 |