Fair Value - Financial Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial Assets and Liabilities Measured on a Recurring Basis
Securities available-for-sale	$ 294,438	$ 404,825
I/O strip receivables	491	503
Agency mortgage-backed securities
Financial Assets and Liabilities Measured on a Recurring Basis
Securities available-for-sale	203,609	284,361
U.S. Treasury
Financial Assets and Liabilities Measured on a Recurring Basis
Securities available-for-sale	90,829	120,464
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury
Financial Assets and Liabilities Measured on a Recurring Basis
Securities available-for-sale	90,829	120,464
Significant Other Observable Inputs (Level 2)
Financial Assets and Liabilities Measured on a Recurring Basis
I/O strip receivables	491	503
Significant Other Observable Inputs (Level 2) | Agency mortgage-backed securities
Financial Assets and Liabilities Measured on a Recurring Basis
Securities available-for-sale	203,609	284,361
Recurring basis
Transfers between Level 1 and Level 2
Transfers between Level 1 and Level 2	0	0
Transfers between Level 2 and Level 1	$ 0	$ 0