Stock-Based Compensation - Early Exercise Of Stock Options (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-Based Compensation
Unvested balance at beginning of period	755	912	1,034
Early exercised	(306)	471	427
Vested	(267)	(628)	(549)
Unvested balance at end of period	182	755	912