Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands |
3 Months Ended | 12 Months Ended | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2017 |
Sep. 30, 2017 |
Jun. 30, 2017 |
Mar. 31, 2017 |
Dec. 31, 2016 |
Sep. 30, 2016 |
Jun. 30, 2016 |
Mar. 31, 2016 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Basic | |||||||||||
| Net income available to common shareholders | $ 2,457 | $ 17,394 | $ 16,926 | $ 15,717 | $ 15,118 | $ 15,138 | $ 14,833 | $ 14,251 | $ 52,494 | $ 59,340 | $ 58,421 |
| Less: income attributable to unvested stock-based compensation awards | (818) | (912) | (834) | ||||||||
| Net earnings allocated to common shareholders | $ 51,676 | $ 58,428 | $ 57,587 | ||||||||
| Weighted average shares outstanding, including unvested stock-based compensation awards (in shares) | 15,193,438 | 15,044,733 | 14,940,274 | ||||||||
| Less: unvested stock-based compensation awards (in shares) | (243,006) | (232,021) | (212,081) | ||||||||
| Weighted average shares outstanding - Basic (in shares) | 14,950,432 | 14,812,712 | 14,728,193 | ||||||||
| Diluted | |||||||||||
| Net earnings allocated to common shareholders | $ 51,676 | $ 58,428 | $ 57,587 | ||||||||
| Weighted average shares outstanding - Basic (in shares) | 14,950,432 | 14,812,712 | 14,728,193 | ||||||||
| Plus: incremental shares from assumed conversion of stock-based compensation awards (in shares) | 122,823 | 123,519 | 134,833 | ||||||||
| Weighted average shares outstanding - Diluted (in shares) | 15,073,255 | 14,936,231 | 14,863,026 | ||||||||
| Basic EPS (in dollars per share) | $ 0.16 | $ 1.14 | $ 1.11 | $ 1.04 | $ 1.00 | $ 1.01 | $ 0.99 | $ 0.95 | $ 3.46 | $ 3.94 | $ 3.91 |
| Diluted EPS (in dollars per share) | $ 0.16 | $ 1.14 | $ 1.11 | $ 1.03 | $ 0.99 | $ 1.00 | $ 0.98 | $ 0.94 | $ 3.43 | $ 3.91 | $ 3.87 |
| Antidilutive securities excluded from computation of earning per share (in shares) | 20,789 | 72,321 | 108,159 | ||||||||