Defined Contribution Plan (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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	$ 2,700,000	$ 2,400,000	$ 2,100,000