Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands |
3 Months Ended | |
|---|---|---|
Mar. 31, 2018 |
Mar. 31, 2017 |
|
| Earnings Per Share [Abstract] | ||
| Net income | $ 41,635 | $ 32,645 |
| Denominator (in thousands): | ||
| Weighted-average common shares for calculating basic earnings per share (shares) | 46,426 | 48,389 |
| Stock options and nonvested stock awards (shares) | 53 | 13 |
| Weighted-average common shares for calculating diluted earnings per share (shares) | 46,479 | 48,402 |
| Net income per share: | ||
| Basic (in dollars per share) | $ 0.90 | $ 0.67 |
| Diluted (in dollars per share) | $ 0.90 | $ 0.67 |