Stock-Based Compensation - (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Stock-based compensation
Stock-based compensation expense	$ 1,700	$ 1,900	$ 4,300	$ 3,900
Proceeds from exercise of stock options			$ 11,112	$ 1,737
Common Stock
Stock-based compensation
Exercise of stock options (in shares)	300,000	200,000	1,900,000	400,000
Proceeds from exercise of stock options	$ 1,800	$ 1,200	$ 11,400	$ 1,700
2000 Stock Plan
Stock-based compensation
Number of shares of common stock available for future grant	0		0