Financial Instruments - Schedule of Assets, Liabilities, and Equity Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Assets
U.S. treasury securities	$ 128,056	$ 70,029
U.S. treasury securities	18,792	30,978
Fair Value, Measurements, Recurring
Assets
Money market funds	314,415
Loans held for sale	42,439	21,985
Derivative asset	1,880	500
U.S. treasury securities	18,792
Total assets	505,582	344,934
Liabilities
Total liabilities	540	115
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Money market funds	314,415
Loans held for sale	0	0
Derivative asset	0	0
U.S. treasury securities	18,792
Total assets	461,263	322,449
Liabilities
Total liabilities	0	0
Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets
Money market funds	0
Loans held for sale	42,439	21,985
Derivative asset	45	4
U.S. treasury securities	0
Total assets	42,484	21,989
Liabilities
Total liabilities	498	57
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
Money market funds	0
Loans held for sale	0	0
Derivative asset	1,835	496
U.S. treasury securities	0
Total assets	1,835	496
Liabilities
Total liabilities	42	58
U.S. treasury securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
U.S. treasury securities	128,056	70,029
U.S. treasury securities	13,783	30,978
U.S. treasury securities \| Fair Value, Measurements, Recurring
Assets
U.S. treasury securities	128,056	70,029
U.S. treasury securities	13,783	30,978
U.S. treasury securities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
U.S. treasury securities	128,056	70,029
U.S. treasury securities	13,783	30,978
U.S. treasury securities \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets
U.S. treasury securities	0	0
U.S. treasury securities	0	0
U.S. treasury securities \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
U.S. treasury securities	0	0
U.S. treasury securities	0	0
Forward sales commitments \| Fair Value, Measurements, Recurring
Assets
Derivative asset	45	4
Liabilities
Derivative liability	498	57
Forward sales commitments \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Forward sales commitments \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets
Derivative asset	45	4
Liabilities
Derivative liability	498	57
Forward sales commitments \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Interest rate lock commitments \| Fair Value, Measurements, Recurring
Assets
Derivative asset	1,835	496
Liabilities
Derivative liability	42	58
Interest rate lock commitments \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Interest rate lock commitments \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Interest rate lock commitments \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
Derivative asset	1,835	496
Liabilities
Derivative liability	42	58
Agency bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
U.S. treasury securities	0
U.S. treasury securities	5,009
Agency bonds \| Fair Value, Measurements, Recurring
Assets
U.S. treasury securities	5,009
Agency bonds \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
U.S. treasury securities	5,009
Agency bonds \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets
U.S. treasury securities	0
Agency bonds \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
U.S. treasury securities	0
Money market funds \| Fair Value, Measurements, Recurring
Assets
Money market funds	310,115	221,442
Money market funds \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Money market funds	310,115	221,442
Money market funds \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets
Money market funds	0	0
Money market funds \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
Money market funds	0	$ 0
U.S. treasury securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Money market funds	4,300
U.S. treasury securities \| Fair Value, Measurements, Recurring
Assets
Money market funds	4,300
U.S. treasury securities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Money market funds	4,300
U.S. treasury securities \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets
Money market funds	0
U.S. treasury securities \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
Money market funds	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as noncurrent.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Fair value of financial obligations, including, but not limited to, debt instruments, derivative liabilities, federal funds purchased and sold under agreements to repurchase, securities loaned or sold under agreements to repurchase, financial instruments sold not yet purchased, guarantees, line of credit, loans and notes payable, servicing liability, and trading liabilities.

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Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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