Stock-Based Compensation - Restricted Stock Unit Activity (Details) - RSUs and PSUs shares in Thousands	9 Months Ended
	Sep. 30, 2021 $ / shares shares
Units
Non-vested, beginning balance (in shares)	7,015
Granted (in shares)	4,791
Vested (in shares)	(1,882)
Forfeited (in shares)	(1,439)
Unvested, ending balance (in shares)	8,485
Weighted-Average Grant Date Fair Value
Non-vested, weighted average grant date fair value, beginning balance (in dollars per share) | $ / shares	$ 1.55
Granted, weighted average grant date fair value (in dollars per share) | $ / shares	1.52
Vested, weighted average grant date fair value (in dollars per share) | $ / shares	1.65
Forfeited, weighted average grant date fair value (in dollars per share) | $ / shares	1.61
Non-vested, weighted average grant date fair value, ending balance (in dollars per share) | $ / shares	$ 1.50
Shares withheld for tax purposes (in shares)	124