Other Non-Operating Income (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended					9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Schedule of Non-Operating Income (Expense) [Line Items]
Gain on acquiring a controlling interest in an equity affiliate	$ 0			$ 0		$ 3,708	$ 0
Gain related to contingent consideration	800					2,500
Gain on cost method investments	1,638	$ 2,600		3,669	$ 1,400	4,209	5,080
Impairment of a cost method investment	0		$ 2,600	0		2,577	0
Gain on sale of equity affiliates	$ 0			$ 0		$ 1,370	$ 28,994
Gimlet Media [Member]
Schedule of Non-Operating Income (Expense) [Line Items]
Gain on sale of equity affiliates					$ 29,000
Framebridge [Member]
Schedule of Non-Operating Income (Expense) [Line Items]
Gain on acquiring a controlling interest in an equity affiliate		$ 3,700