Investments - Maturities of AFS Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Amortized Cost
Within one year	$ 45,957
After one, but within five years	301,995
After five, but within ten years	231,164
Greater than ten years	380,734
Amortized Cost	959,850	$ 966,900
Fair Value
Within one year	46,277
After one, but within five years	314,345
After five, but within ten years	244,374
Greater than ten years	397,974
Total	$ 1,002,970	$ 978,284