Financial Instruments - Schedule of Assets, Liabilities, and Equity Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets
Cash and cash equivalents, fair value disclosure	$ 342,172
U.S. treasury securities	129,809	$ 70,029
Loans held for sale	41,921	21,985
Derivative asset	2,728	500
U.S. treasury securities	17,072	30,978
Total assets	533,702	344,934
Liabilities
Total liabilities	427	115
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash and cash equivalents, fair value disclosure	342,172
Loans held for sale	0	0
Derivative asset	0	0
U.S. treasury securities	17,072
Total assets	489,053	322,449
Liabilities
Total liabilities	0	0
Significant Other Observable Inputs (Level 2)
Assets
Cash and cash equivalents, fair value disclosure	0
Loans held for sale	41,921	21,985
Derivative asset	763	4
U.S. treasury securities	0
Total assets	42,684	21,989
Liabilities
Total liabilities	23	57
Significant Unobservable Inputs (Level 3)
Assets
Cash and cash equivalents, fair value disclosure	0
Loans held for sale	0	0
Derivative asset	1,965	496
U.S. treasury securities	0
Total assets	1,965	496
Liabilities
Total liabilities	404	58
U.S. treasury securities
Assets
U.S. treasury securities	129,809	70,029
U.S. treasury securities	5,150	30,978
U.S. treasury securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
U.S. treasury securities	129,809	70,029
U.S. treasury securities	5,150	30,978
U.S. treasury securities \| Significant Other Observable Inputs (Level 2)
Assets
U.S. treasury securities	0	0
U.S. treasury securities	0	0
U.S. treasury securities \| Significant Unobservable Inputs (Level 3)
Assets
U.S. treasury securities	0	0
U.S. treasury securities	0	0
Forward sales commitments
Assets
Derivative asset	763	4
Liabilities
Derivative liability	23	57
Forward sales commitments \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Forward sales commitments \| Significant Other Observable Inputs (Level 2)
Assets
Derivative asset	763	4
Liabilities
Derivative liability	23	57
Forward sales commitments \| Significant Unobservable Inputs (Level 3)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Interest rate lock commitments
Assets
Derivative asset	1,965	496
Liabilities
Derivative liability	404	58
Interest rate lock commitments \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Interest rate lock commitments \| Significant Other Observable Inputs (Level 2)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
Interest rate lock commitments \| Significant Unobservable Inputs (Level 3)
Assets
Derivative asset	1,965	496
Liabilities
Derivative liability	404	58
Agency bonds
Assets
U.S. treasury securities	0
U.S. treasury securities	11,922
Agency bonds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
U.S. treasury securities	11,922
Agency bonds \| Significant Other Observable Inputs (Level 2)
Assets
U.S. treasury securities	0
Agency bonds \| Significant Unobservable Inputs (Level 3)
Assets
U.S. treasury securities	0
Money market funds
Assets
Cash and cash equivalents, fair value disclosure	336,821	221,442
Money market funds \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash and cash equivalents, fair value disclosure	336,821	221,442
Money market funds \| Significant Other Observable Inputs (Level 2)
Assets
Cash and cash equivalents, fair value disclosure	0	0
Money market funds \| Significant Unobservable Inputs (Level 3)
Assets
Cash and cash equivalents, fair value disclosure	0	$ 0
U.S. treasury securities \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash and cash equivalents, fair value disclosure	5,351
U.S. treasury securities \| Significant Other Observable Inputs (Level 2)
Assets
Cash and cash equivalents, fair value disclosure	0
U.S. treasury securities \| Significant Unobservable Inputs (Level 3)
Assets
Cash and cash equivalents, fair value disclosure	$ 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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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 portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

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