Summary of Significant Accounting Policies (Cash and Cash Equivalents and Accounts Receivable) (Details) $ in Thousands	Dec. 31, 2020 USD ($) Integer	Jan. 03, 2020 USD ($)	Dec. 31, 2019 USD ($)
Accounting Policies [Abstract]
Money Market Funds, at Carrying Value	$ 51,500		$ 443,200
Restricted Cash, Current	25,121	$ 24,700	0
Bank overdrafts	$ 1,600		$ 1,600
Number of types of accounts receivable | Integer	3