Defined Contribution Plan (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Contribution Plan [Abstract]
Condition to participate in defined contribution plan	Employees have the opportunity to participate following completion of three months of employment and must be 21 years of age.
Discretionary matching contribution company percentage	75.00%
Discretionary matching contribution, employee's contribution, maximum	$ 4,000
Company matching contributions	$ 2,100,000	$ 2,000,000	$ 2,000,000