Investments - Trading Securities (Details) - Trading Securities. - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2019
Jun. 30, 2018
Jun. 30, 2019
Jun. 30, 2018
Dec. 31, 2018
Investments          
Cost $ 16,572   $ 16,572   $ 14,874
Gross unrealized gains     331   5
Gross unrealized losses     (800)   (2,160)
Trading securities, at fair value 16,103   16,103   $ 12,719
Proceeds and realized gains and losses recognized          
Sale Proceeds 865 $ 180 1,435 $ 628  
Realized gains 12 5 14 33  
Realized losses $ (12) $ (4) $ (31) $ (6)