Equity Compensation (Expense) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Stock options
Total stock-based compensation expense
Total stock-based compensation expense	$ 3,529	$ 3,335
Total unrecognized compensation cost related to non-vested stock option awards	$ 600
Weighted-average period over which unrecognized compensation cost will be recognized	3 months 18 days
Stock options | Cost of revenue
Total stock-based compensation expense
Total stock-based compensation expense	$ 78	68
Stock options | Research and development
Total stock-based compensation expense
Total stock-based compensation expense	1,287	1,084
Stock options | Sales and marketing
Total stock-based compensation expense
Total stock-based compensation expense	870	959
Stock options | General and administrative
Total stock-based compensation expense
Total stock-based compensation expense	1,294	$ 1,224
Restricted stock units
Total stock-based compensation expense
Total unrecognized compensation cost related to non-vested restricted stock units	$ 18,000
Weighted-average period over which unrecognized compensation cost will be recognized	2 years 3 months 18 days