Separation Agreement - Severance and Vacation Pay (Details) - USD ($) $ in Millions		12 Months Ended
	Apr. 22, 2015	Dec. 31, 2017	Dec. 31, 2015
General and administrative expenses
Separation Agreement
Accelerated vesting charge (in dollars)			$ 0.5
General and administrative expenses | Chief Financial Officer
Separation Agreement
Severance Costs		$ 0.5
General and administrative expenses | Chief Executive Officer
Separation Agreement
Severance Costs			$ 0.5
Employee Stock Options | Chief Executive Officer
Separation Agreement
Accelerated vesting (in shares)	53,820