Financial Instruments - Schedule of Assets, Liabilities, and Equity Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Assets
Cash equivalents	$ 617,502	$ 892,361
U.S. treasury securities	140,843	131,561
Loans held for sale	43,447	42,539
Other current assets	3,611	1,815
Long-term investments	6,906	11,922
Total assets	812,309	1,080,198
Liabilities
Financial and Nonfinancial Liabilities, Fair Value Disclosure	219	517
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash equivalents	617,502	892,361
Loans held for sale	0	0
Other current assets	0	0
Total assets	765,251	1,035,844
Liabilities
Financial and Nonfinancial Liabilities, Fair Value Disclosure	0	0
Significant Other Observable Inputs (Level 2)
Assets
Cash equivalents	0	0
Loans held for sale	43,447	42,539
Other current assets	1,465	34
Total assets	44,912	42,573
Liabilities
Financial and Nonfinancial Liabilities, Fair Value Disclosure	10	507
Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents	0	0
Loans held for sale	0	0
Other current assets	2,146	1,781
Total assets	2,146	1,781
Liabilities
Financial and Nonfinancial Liabilities, Fair Value Disclosure	209	10
Money market funds
Assets
Cash equivalents	612,590	886,261
Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash equivalents	612,590	886,261
Money market funds | Significant Other Observable Inputs (Level 2)
Assets
Cash equivalents	0	0
Money market funds | Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents	0	0
U.S. treasury securities
Assets
Cash equivalents	4,912	6,100
U.S. treasury securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash equivalents	4,912	6,100
U.S. treasury securities | Significant Other Observable Inputs (Level 2)
Assets
Cash equivalents	0	0
U.S. treasury securities | Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents	0	0
Agency bonds
Assets
U.S. treasury securities	0	0
Long-term investments	6,906	11,922
Agency bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Long-term investments	6,906	11,922
Agency bonds | Significant Other Observable Inputs (Level 2)
Assets
Long-term investments	0	0
Agency bonds | Significant Unobservable Inputs (Level 3)
Assets
Long-term investments	0	0
U.S. treasury securities
Assets
U.S. treasury securities	140,843	131,561
Long-term investments	0	0
U.S. treasury securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
U.S. treasury securities	140,843	131,561
U.S. treasury securities | Significant Other Observable Inputs (Level 2)
Assets
U.S. treasury securities	0	0
U.S. treasury securities | Significant Unobservable Inputs (Level 3)
Assets
U.S. treasury securities	0	0
IRLCs
Assets
Other current assets	2,146	34
Liabilities
Derivative Liability	209	10
IRLCs | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Other current assets	0	0
Liabilities
Derivative Liability	0	0
IRLCs | Significant Other Observable Inputs (Level 2)
Assets
Other current assets	0	34
Liabilities
Derivative Liability	0	0
IRLCs | Significant Unobservable Inputs (Level 3)
Assets
Other current assets	2,146	0
Liabilities
Derivative Liability	209	10
Forward sales commitments
Assets
Other current assets	1,465	1,781
Liabilities
Derivative Liability	10	507
Forward sales commitments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Other current assets	0	0
Liabilities
Derivative Liability	0	0
Forward sales commitments | Significant Other Observable Inputs (Level 2)
Assets
Other current assets	1,465	0
Liabilities
Derivative Liability	10	507
Forward sales commitments | Significant Unobservable Inputs (Level 3)
Assets
Other current assets	0	1,781
Liabilities
Derivative Liability	$ 0	$ 0