Employee Benefit Plan (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Employer Contribution on employee benefit plan	$ 2.6	$ 2.5	$ 1.3
First 6% of Employee Contribution
Defined Benefit Plan Disclosure [Line Items]
Employer contribution rate as a percentage of employee contribution		50.00%
Percentage contribution from employees			6.00%
First 1% Percent of Contributions
Defined Benefit Plan Disclosure [Line Items]
Employer contribution rate as a percentage of employee contribution		100.00%
Percentage contribution from employees		1.00%
Next 5 % Percent of Employee Contributions
Defined Benefit Plan Disclosure [Line Items]
Employer contribution rate as a percentage of employee contribution		50.00%
Percentage contribution from employees		5.00%