Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Stock-Based Compensation
Stock-based compensation expense	$ 2,900			$ 2,100			$ 7,700	$ 6,100
Proceeds from exercise of stock options							$ 7,740	$ 3,039
Common Stock
Stock-Based Compensation
Exercise of stock options (in shares)	53,000	343,000	1,000	97,000	104,000	288,000
Common Stock | Employee stock purchase plan
Stock-Based Compensation
Exercise of stock options (in shares)	100,000						1,300,000	700,000
Proceeds from exercise of stock options	$ 500			$ 600			$ 8,300	$ 3,400
2000 Stock Plan
Stock-Based Compensation
Number of shares of common stock available for future grants	0						0
Options Expiration period							10 years