Discontinued Operations - Income (loss) from Discontinued Operations, net of tax (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Major classes of line items constituting pretax loss of discontinued operations
Income (loss) from discontinued operations, including gain on sale, net of tax	$ 202,880	$ (1,018)	$ (3,943)	$ (4,042)	$ 104,091	$ (8,649)	$ (7,635)	$ (8,408)	$ 193,877	$ 79,399	$ (67,569)
Net income (loss) from discontinued operations	$ 203,926	$ (594)	$ (3,480)	$ (3,560)	$ 105,439	$ (7,630)	$ (6,818)	$ (7,356)	196,292	83,635	(63,304)
GovDelivery | Discontinued Operations, Disposed of by Sale
Major classes of line items constituting pretax loss of discontinued operations
Revenue									121,917	142,019	133,421
Cost of revenue									(30,180)	(41,255)	(39,229)
Selling, general, administrative and other operating expenses									(105,930)	(132,353)	(161,379)
Other non-major income and expense items									(606)	(520)	(9)
Gain on sale of discontinued operations									220,644	124,840	0
Total discontinued operations before income taxes									205,845	92,731	(67,196)
Income tax (expense) benefit									(11,968)	(13,332)	(373)
Income (loss) from discontinued operations, including gain on sale, net of tax									193,877	79,399	(67,569)
Plus: discontinued operations attributable to noncontrolling interests									2,415	4,236	4,265
Net income (loss) from discontinued operations									$ 196,292	$ 83,635	$ (63,304)