Stock-Based Compensation - Expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Stock-Based Compensation
Total stock-based compensation	$ 2.4	$ 2.7	$ 4.9	$ 5.3
Costs of product revenue
Stock-Based Compensation
Total stock-based compensation	0.3	0.4	0.7	0.8
Selling, general and administrative
Stock-Based Compensation
Total stock-based compensation	1.8	1.9	3.5	3.7
Research and development
Stock-Based Compensation
Total stock-based compensation	0.3	0.4	0.7	0.8
Stock options
Stock-Based Compensation
Total stock-based compensation	1.0	1.7	2.0	3.4
Restricted stock awards
Stock-Based Compensation
Total stock-based compensation	0.2	0.4	0.4	0.7
Restricted stock units
Stock-Based Compensation
Total stock-based compensation	$ 1.2	$ 0.6	$ 2.5	$ 1.2