Income Taxes (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Income Taxes        
Federal income tax at U.S. statutory rate 23.70% 25.30% 24.30% 25.30%
Income Tax Expense (Benefit) $ 4,478 $ 6,311 $ 9,285 $ 9,868
Valuation allowance, deferred tax assets $ 0 $ 0 $ 0 $ 0