Commitments and Contingencies - Employee Benefit Plans, Letters of Credit, and Non-Income Related Taxes (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) draw	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2020 USD ($)
Other Commitments [Line Items]
Employer matching contribution, percent of match			50.00%
Employer matching contribution percent of eligible compensation			5.00%
Employer contribution limit			$ 6,000
Employer contribution vesting period			5 years
Employer matching contributions	$ 3,100,000	$ 3,200,000	$ 1,600,000
Estimated sales tax liability, including interest, minimum				$ 2,500,000
Estimated sales tax liability, including interest, maximum				6,300,000
Accrued sales tax, including interest				$ 2,500,000
Letter of Credit
Other Commitments [Line Items]
Number of draws | draw	2
Proceeds from amounts drawn against letters of credit	$ 1,800,000
Letter of Credit | LOC for office space
Other Commitments [Line Items]
Letters of credit outstanding	100,000
Letter of Credit | LOC for security deposit
Other Commitments [Line Items]
Letters of credit outstanding	$ 100,000
Match Step One
Other Commitments [Line Items]
Employer matching contribution, percent of match	100.00%
Employer matching contribution percent of eligible compensation	3.00%
Match Step Two
Other Commitments [Line Items]
Employer matching contribution, percent of match	50.00%
Employer matching contribution percent of eligible compensation	2.00%