Employee Benefit Plan (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation And Retirement Disclosure Abstract
Defined Contribution Plan Maximum Annual Contributions Per Employee Amount	$ 18,000
Defined Contribution Plan Cost Recognized	$ 835,000	$ 792,000	$ 808,000