Arbitrage Trading Account (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Trading Securities and Derivative Instruments [Abstract]
Arbitrage trading account	$ 400,809	$ 452,548
Options Held | Long
Derivative [Line Items]
Other derivatives not designated as hedging instruments at fair value, net	9
Derivative, notional amount	15,500
Options Held | Short
Derivative [Line Items]
Other derivatives not designated as hedging instruments at fair value, net	56
Derivative, notional amount	$ 17,100