|
Share-based compensation plans (Details) (USD $)
In Millions, except Share data, unless otherwise specified
|
3 Months Ended |
9 Months Ended |
|
Sep. 30, 2012
|
Sep. 30, 2011
|
Sep. 30, 2012
|
Sep. 30, 2011
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |
|
|
|
|
| Number of shares underlying options |
182,000 |
290,000 |
389,000 |
290,000 |
| Weighted-average exercise price per share |
$ 22.56 |
$ 31.47 |
$ 22.47 |
$ 31.47 |
| Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |
|
|
|
|
| Expected dividend yield - weighted average |
1.80% |
1.30% |
1.80% |
1.30% |
| Expected dividend yield - range |
1.8 |
1.3 |
1.8 |
1.3 |
| Expected volatility - weighted average |
40.00% |
36.00% |
40.00% |
36.00% |
| Expected volatility range - minimum |
|
36.00% |
|
36.00% |
| Expected volatility range - maximum |
40.00% |
37.00% |
40.00% |
37.00% |
| Risk-free interest rate - weighted average |
0.60% |
1.20% |
0.70% |
1.20% |
| Risk-free interest rate range - minimum |
0.40% |
0.50% |
0.40% |
0.50% |
| Risk-free interest rate range - maximum |
0.80% |
1.90% |
0.90% |
1.90% |
| Share Based Compensation Arrangement By Share Based Payment Award Options Grants In Period Aggregate Weighted Average Grant Date Fair Value |
$ 1.2 |
$ 2.4 |
$ 2.5 |
$ 2.4 |
| Weighted-average fair value estimates at grant date |
$ 6.31 |
$ 8.17 |
$ 6.30 |
$ 8.17 |
| Nonvested share activity [Rollforward] |
|
|
|
|
| Beginning balance - shares |
|
|
315,400 |
|
| Stock units granted - shares |
|
|
338,100 |
|
| Cancelled awards - shares |
|
|
(13,500) |
|
| Vested - shares |
|
|
(200,700) |
|
| Ending balance - shares |
439,300 |
|
439,300 |
|
|
Weighted Average [Memeber]
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |
|
|
|
|
| Expected term in years |
4 years 3 months 0 days |
3 years 9 months 11 days |
4 years 3 months 0 days |
3 years 9 months 11 days |
|
Minimum [Member]
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |
|
|
|
|
| Expected term in years |
3 years 3 months 0 days |
1 year 10 months 15 days |
3 years 3 months 0 days |
1 year 10 months 15 days |
|
Maximum [Member]
|
|
|
|
|
| Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] |
|
|
|
|
| Expected term in years |
5 years 3 months 0 days |
5 years 3 months 0 days |
5 years 3 months 0 days |
5 years 3 months 0 days |
|
2005 Equity Incentive Plan
|
|
|
|
|
| Nonvested share activity [Rollforward] |
|
|
|
|
| Beginning balance - shares |
|
|
299,600 |
|
| Stock units granted - shares |
|
|
315,100 |
|
| Cancelled awards - shares |
|
|
(13,500) |
|
| Vested - shares |
|
|
(184,900) |
|
| Ending balance - shares |
416,300 |
|
416,300 |
|
| Weighted-average grant-date fair value [Rollforward] |
|
|
|
|
| Beginning Balance - grant-date fair value |
|
|
$ 25.99 |
|
| Stock units granted - grant-date fair value |
|
|
$ 22.13 |
|
| Cancelled awards - grant-date fair value |
|
|
$ 24.85 |
|
| Vested - grant-date fair value |
|
|
$ 25.69 |
|
| Ending Balance - grant-date fair value |
$ 23.20 |
|
$ 23.20 |
|
|
Non-Employee Directors' Equity Plan
|
|
|
|
|
| Nonvested share activity [Rollforward] |
|
|
|
|
| Beginning balance - shares |
|
|
15,800 |
|
| Stock units granted - shares |
|
|
23,000 |
|
| Cancelled awards - shares |
|
|
0 |
|
| Vested - shares |
|
|
(15,800) |
|
| Ending balance - shares |
23,000 |
|
23,000 |
|
| Weighted-average grant-date fair value [Rollforward] |
|
|
|
|
| Beginning Balance - grant-date fair value |
|
|
$ 25.99 |
|
| Stock units granted - grant-date fair value |
|
|
$ 22.13 |
|
| Cancelled awards - grant-date fair value |
|
|
$ 24.85 |
|
| Vested - grant-date fair value |
|
|
$ 25.69 |
|
| Ending Balance - grant-date fair value |
$ 23.20 |
|
$ 23.20 |
|