Fair Value - Financial Assets and Liabilities Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial Assets and Liabilities Measured on a Recurring Basis
Securities available-for-sale	$ 235,774	$ 404,825
I/O strip receivables	305	503
Agency mortgage-backed securities
Financial Assets and Liabilities Measured on a Recurring Basis
Securities available-for-sale	175,326	284,361
U.S. Treasury
Financial Assets and Liabilities Measured on a Recurring Basis
Securities available-for-sale	60,448	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	60,448	120,464
Significant Other Observable Inputs (Level 2)
Financial Assets and Liabilities Measured on a Recurring Basis
I/O strip receivables	305	503
Significant Other Observable Inputs (Level 2) | Agency mortgage-backed securities
Financial Assets and Liabilities Measured on a Recurring Basis
Securities available-for-sale	$ 175,326	$ 284,361