Income Taxes (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Income tax reconciliation    
Earnings before income taxes $ 24,937 $ 14,868
Income taxes at statutory rate 5,237 5,204
Dividends-received deduction (25) (79)
Tax-exempt interest (279) (633)
Other (80) (134)
Provision for income taxes as shown on the Consolidated Statements of Earnings $ 4,853 $ 4,358
GAAP effective tax rate (percent) 19.50% 29.30%