Fair Value Measurements - Changes in Private Placement Warrants Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Adjustment of Warrants	$ (83,013)			$ 144,753			$ (113,207)	$ 224,175
Stock Issued During Period, Value, Private Warrants Exercised			$ (3,592)
Warrants and Rights Outstanding	195,952						195,952		$ 312,751
Level 3 | Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrants and Rights Outstanding	195,952	$ 278,965	257,944	335,988	$ 191,235	$ 167,445	$ 195,952	$ 335,988	$ 312,751	$ 111,813
Level 3 | Recurring | Private Warrant
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Adjustment of Warrants	(83,013)	21,021	(51,215)	$ 144,753	$ 23,790	$ 55,632
Stock Issued During Period, Value, Private Warrants Exercised	$ 0	$ 0	$ (3,592)