Stock Incentive Plan (Schedule of Share-based Compensation, Unearned Compensation Related to RSU's) (Details) - Restricted Stock Units (RSUs) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Changes In Unearned Compensation [Roll Forward]
Unearned compensation at beginning of year	$ 128,390	$ 129,669	$ 122,910
RSUs granted, net of cancellations	54,270	53,583	52,204
RSUs expensed	47,108	(47,329)	(34,408)
RSUs forfeitures	3,242	(7,533)	(11,037)
Unearned compensation at end of year	$ 132,310	$ 128,390	$ 129,669