Stock-Based Compensation - Early Exercise Of Stock Options (Details) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-Based Compensation
Unvested balance at beginning of period	912	1,034	7,159
Early exercised	471	427	830
Vested	(628)	(549)	(6,955)
Unvested balance at end of period	755	912	1,034