Financial Instruments - Schedule of Assets, Liabilities, and Equity Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Assets
U.S. treasury securities		$ 70,029
U.S. treasury securities		30,978
Fair Value, Measurements, Recurring
Assets
Money market funds	$ 892,361
U.S. treasury securities	131,561
Loans held for sale	42,539	21,985
Derivative asset	1,815	500
U.S. treasury securities	11,922
Total assets	1,080,198	344,934
Liabilities
Total liabilities	517	115
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Money market funds	892,361
Loans held for sale	0	0
Derivative asset	0	0
Total assets	1,035,844	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	42,539	21,985
Derivative asset	34	4
Total assets	42,573	21,989
Liabilities
Total liabilities	507	57
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
Money market funds	0
Loans held for sale	0	0
Derivative asset	1,781	496
Total assets	1,781	496
Liabilities
Total liabilities	10	58
U.S. treasury securities \| Fair Value, Measurements, Recurring
Assets
U.S. treasury securities	131,561	70,029
U.S. treasury securities		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	131,561	70,029
U.S. treasury securities		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
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
Forward sales commitments \| Fair Value, Measurements, Recurring
Assets
Derivative asset	34	4
Liabilities
Derivative liability	507	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	34	4
Liabilities
Derivative liability	507	57
Forward sales commitments \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
IRLCs \| Fair Value, Measurements, Recurring
Assets
Derivative asset	1,781	496
Liabilities
Derivative liability	10	58
IRLCs \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
IRLCs \| Fair Value, Measurements, Recurring \| Significant Other Observable Inputs (Level 2)
Assets
Derivative asset	0	0
Liabilities
Derivative liability	0	0
IRLCs \| Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Assets
Derivative asset	1,781	496
Liabilities
Derivative liability	10	58
Agency bonds \| Fair Value, Measurements, Recurring
Assets
U.S. treasury securities	11,922
Agency bonds \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
U.S. treasury securities	11,922
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	886,261	221,442
Money market funds \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Money market funds	886,261	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 \| Fair Value, Measurements, Recurring
Assets
Money market funds	6,100
U.S. treasury securities \| Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Money market funds	6,100
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

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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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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 of financial and nonfinancial obligations.

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