Fair Value Measurements - Assets Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities, available for sale	$ 450,538	$ 339,937
U.S. Treasuries
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities, available for sale	47,700	0
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities, available for sale	450,538	339,937
Fair Value, Measurements, Recurring | Level 1: Quoted Prices in Active Markets For Identical Assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities, available for sale	47,700	0
Fair Value, Measurements, Recurring | Level 2: Significant Other Observable Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities, available for sale	390,024	330,539
Fair Value, Measurements, Recurring | Level 3: Significant Unobservable Inputs
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities, available for sale	$ 12,814	$ 9,398