| Three Months Ended September 30, | Nine Months Ended September 30, | |||||||||||||||||||||||||
| 2020 | 2019 | 2020 | 2019 | |||||||||||||||||||||||
| Basic: | ||||||||||||||||||||||||||
| Net income | $ | 36,474 | $ | 25,454 | $ | 85,524 | $ | 151,442 | ||||||||||||||||||
| Weighted average number of common shares during the period (in thousands) | 41,916 | 41,785 | 41,865 | 41,715 | ||||||||||||||||||||||
| Net income per share – basic | $ | 0.87 | $ | 0.61 | $ | 2.04 | $ | 3.63 | ||||||||||||||||||
| Diluted: | ||||||||||||||||||||||||||
| Net income | $ | 36,474 | $ | 25,454 | $ | 85,524 | $ | 151,442 | ||||||||||||||||||
| Weighted average number of common shares during the period | 41,916 | 41,785 | 41,865 | 41,715 | ||||||||||||||||||||||
| Weighted average number of common equivalent shares to reflect the dilutive effect of common stock equivalent securities: | ||||||||||||||||||||||||||
| Stock options | 33 | 100 | 45 | 80 | ||||||||||||||||||||||
| Common stock units related to deferred compensation for employees | — | — | — | |||||||||||||||||||||||
| Restricted common stock units related to incentive compensation | 109 | 145 | 103 | 116 | ||||||||||||||||||||||
Total common and common equivalent shares adjusted to calculate diluted earnings per share | 42,058 | 42,030 | 42,013 | 41,911 | ||||||||||||||||||||||
| Net income per share – diluted | $ | 0.87 | $ | 0.60 | $ | 2.03 | $ | 3.61 | ||||||||||||||||||