Income Taxes (Net Operating Loss Carryforwards) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($)
Net operating loss carryforwards
Net operating losses related to stock option benefits	$ 31.6
Federal
Net operating loss carryforwards
Net operating loss carryforwards	148.8
Federal | Research and development.
Net operating loss carryforwards
Research and development tax credit carryforwards	12.0
State
Net operating loss carryforwards
Net operating loss carryforwards	97.0
State | Research and development.
Net operating loss carryforwards
Research and development tax credit carryforwards	$ 11.1