Investment Securities - Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Amortized Cost
Within one year	$ 78,072
After one year but within five years	174,886
Amortized Cost	252,958	$ 251,810
Fair value
Within one year	78,326
After one year but within five years	177,942
Total fair value	256,268	$ 250,764
Fair value
Within one year	30,749
After one year but within five years	78,367
After five years but within 10 years	28,032
Total fair value	$ 137,148