Earnings Per Share (Components of Basic and Diluted Earnings Per Share) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Nov. 15, 2019	Jun. 10, 2014
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Net income	$ 60,883	$ 30,745	$ 92,580	$ 95,783
Net income available to participating securities	(89)	(511)	(477)	(1,361)
Net income available to J2 Global, Inc. common shareholders	$ 60,794	$ 30,234	$ 92,103	$ 94,422
Denominator:
Weighted-average outstanding shares of common stock - basic (in shares)	46,279,515	47,673,211	46,914,750	47,654,327
Dilutive effect of:
Dilutive effect of equity incentive plans (in shares)	29,557	68,413	23,211	73,906
Dilutive effect of convertible debt (in shares)	0	1,322,648	682,347	1,164,290
Common stock and common stock equivalents (in shares)	46,309,072	49,064,272	47,620,308	48,892,523
Net income per share:
Basic (in usd per share)	$ 1.31	$ 0.63	$ 1.96	$ 1.98
Diluted (in usd per share)	$ 1.31	$ 0.62	$ 1.93	$ 1.93
3.25% Convertible Notes | Convertible Debt
Net income per share:
Stated interest rate						3.25%
1.75% Convertible Notes | Convertible Debt
Net income per share:
Stated interest rate					1.75%