Financial Instruments - Schedule of Assets, Liabilities, and Equity Measured at Fair Value on a Recurring Basis (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Assets
Cash equivalents	$ 632,800	$ 892,361
Short-term investments	29,605	131,561
Loans held for sale	51,643	42,539
Other current assets	2,032	1,815
Long-term investments	36,085	11,922
Total assets	752,165	1,080,198
Liabilities
Total liabilities	454	517
Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash equivalents	632,800	892,361
Loans held for sale	0	0
Other current assets	0	0
Total assets	698,490	1,035,844
Liabilities
Total liabilities	0	0
Significant Other Observable Inputs (Level 2)
Assets
Cash equivalents	0	0
Loans held for sale	51,643	42,539
Other current assets	36	34
Total assets	51,679	42,573
Liabilities
Total liabilities	430	507
Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents	0	0
Loans held for sale	0	0
Other current assets	1,996	1,781
Total assets	1,996	1,781
Liabilities
Total liabilities	24	10
Money market funds
Assets
Cash equivalents	632,800	886,261
Money market funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash equivalents	632,800	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		6,100
U.S. treasury securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Cash equivalents		6,100
U.S. treasury securities | Significant Other Observable Inputs (Level 2)
Assets
Cash equivalents		0
U.S. treasury securities | Significant Unobservable Inputs (Level 3)
Assets
Cash equivalents		0
Agency bonds
Assets
Short-term investments	5,007	0
Long-term investments	6,907	11,922
Agency bonds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Short-term investments	5,007
Long-term investments	6,907	11,922
Agency bonds | Significant Other Observable Inputs (Level 2)
Assets
Short-term investments	0
Long-term investments	0	0
Agency bonds | Significant Unobservable Inputs (Level 3)
Assets
Short-term investments	0
Long-term investments	0	0
U.S. treasury securities
Assets
Short-term investments	24,598	131,561
Long-term investments	29,178	0
U.S. treasury securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets
Short-term investments	24,598	131,561
Long-term investments	29,178
U.S. treasury securities | Significant Other Observable Inputs (Level 2)
Assets
Short-term investments	0	0
Long-term investments	0
U.S. treasury securities | Significant Unobservable Inputs (Level 3)
Assets
Short-term investments	0	0
Long-term investments	0
IRLCs
Assets
Other current assets	1,996	1,781
Liabilities
Derivative Liability	24	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	0
Liabilities
Derivative Liability	0	0
IRLCs | Significant Unobservable Inputs (Level 3)
Assets
Other current assets	1,996	1,781
Liabilities
Derivative Liability	24	10
Forward sales commitments
Assets
Other current assets	36	34
Liabilities
Derivative Liability	430	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	36	34
Liabilities
Derivative Liability	430	507
Forward sales commitments | Significant Unobservable Inputs (Level 3)
Assets
Other current assets	0	0
Liabilities
Derivative Liability	$ 0	$ 0