Significant Accounting Policies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Impairment charges on minority investments	$ 2,361,000	$ 927,000
Carrying amount of cost method investments	5,016,000	8,327,000
Finite lives impairment charge	0	0
Advertising costs	$ 7,561,000	$ 13,732,000	$ 13,562,000