Stock-Based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock-Based Compensation
Stock-based compensation expense	$ 3,100		$ 2,300		$ 4,800	$ 4,000
Proceeds from exercise of stock options					$ 7,282	$ 2,396
Common Stock
Stock-Based Compensation
Exercise of stock options (in shares)	343,000	540,000	104,000	288,000
Common Stock | Employee stock purchase plan
Stock-Based Compensation
Exercise of stock options (in shares)	600,000		300,000		1,200,000	600,000
Proceeds from exercise of stock options	$ 3,300		$ 1,000		$ 7,800	$ 2,800
2000 Stock Plan
Stock-Based Compensation
Number of shares of common stock available for future grants	0				0
Options Expiration period					10 years