Income Taxes (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
Dec. 31, 2017 |
|
| Income Taxes | |||||
| Federal income tax at U.S. statutory rate | 21.00% | 35.00% | |||
| Provisional credit to federal tax expense | $ (2,400) | ||||
| Provision for income taxes | $ 6,562 | $ 5,126 | $ 16,430 | $ 9,320 | |
| Effective income tax rate ( as a percent) | 24.20% | 39.50% | 24.80% | 38.90% | |
| Valuation allowance, deferred tax assets | $ 0 | $ 0 | $ 0 | $ 0 | |