Investment Securities - Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Amortized Cost
Within one year	$ 64,321
After one year but within five years	121,170
Amortized Cost	185,491	$ 252,958
Fair value
Within one year	65,057
After one year but within five years	124,860
Total fair value	189,917	$ 256,268
Fair value
Within one year	29,580
After one year but within five years	83,508
After five years but within 10 years	21,665
Total fair value	$ 134,753