Net Income Per Share: (Details) (USD $) In Thousands, except Share data | 3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2011 | Sep. 30, 2010 | Sep. 30, 2011 | Sep. 30, 2010 | |
| Earnings Per Share [Abstract] | ||||
| Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount | 295,000 | 559,000 | 189,000 | 742,000 |
| Net income | $ 9,261 | $ 8,975 | $ 26,827 | $ 20,943 |
| Weighted average number of common shares outstanding (for basic calculation) | 13,932,000 | 13,489,000 | 13,826,000 | 13,605,000 |
| Dilutive securities | 252,000 | 263,000 | 343,000 | 233,000 |
| Weighted average common and common equivalent shares outstanding (for diluted calculation) | 14,184,000 | 13,752,000 | 14,169,000 | 13,838,000 |
| EPS - basic | $ 0.66 | $ 0.67 | $ 1.94 | $ 1.54 |
| EPS - diluted | $ 0.65 | $ 0.65 | $ 1.89 | $ 1.51 |