Arbitrage Trading Account (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Trading Securities and Derivative Instruments [Abstract]
Arbitrage trading account	$ 341,473	$ 400,809
Options Held | Long
Derivative [Line Items]
Other derivatives not designated as hedging instruments at fair value, net	0
Derivative, notional amount	12,000
Options Held | Short
Derivative [Line Items]
Other derivatives not designated as hedging instruments at fair value, net	326
Derivative, notional amount	$ 3,200