Stock-Based Compensation - (Details) - USD ($) $ in Thousands, shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Stock-based compensation
Stock-based compensation expense	$ 1,500	$ 1,200	$ 2,600	$ 2,100
Proceeds from exercise of stock options			$ 9,290	$ 556
Common Stock
Stock-based compensation
Exercise of stock options (in shares)	1.2	0.3	1.7	0.6
Proceeds from exercise of stock options	$ 7,100	$ 400	$ 9,600	$ 600
2000 Stock Plan
Stock-based compensation
Number of shares of common stock available for future grant	0.0		0.0