Segment Information Reportable Segment Information (Reconciliation of Total Segment Operating Income to Consolidated Operating Income) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Total revenues	$ 292,724	$ 273,616	$ 861,236	$ 801,458
Gross Profit	243,507	231,245	716,124	675,119
Direct Costs By Segment	186,451	168,288	558,527	505,627
Income from operations	57,057	62,957	157,596	169,492
Global Operating Costs	(7,053)	(5,534)	(21,379)	(20,035)
Depreciation, Depletion and Amortization, Nonproduction	46,375	39,372	132,850	118,597
Cloud Services Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	150,094	145,787	449,876	432,039
Gross Profit	118,326	115,675	356,427	342,895
Direct Costs By Segment	61,237	59,550	184,266	172,371
Income from operations	57,089	56,125	172,161	170,524
Depreciation, Depletion and Amortization, Nonproduction	15,046	17,145	44,236	51,097
Digital Media Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	142,655	127,865	411,407	369,470
Gross Profit	125,206	115,600	359,745	332,269
Direct Costs By Segment	118,185	103,234	352,931	313,266
Income from operations	7,021	12,366	6,814	19,003
Depreciation, Depletion and Amortization, Nonproduction	30,580	22,227	85,751	67,500
Intersegment Elimination [Member]
Segment Reporting Information [Line Items]
Total revenues	(27)	(36)	(51)	(51)
Gross Profit	(27)	(30)	(52)	(45)
Direct Costs By Segment	(27)	(30)	(52)	(45)
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Total revenues	2	0	4	0
Gross Profit	2	0	4	0
Direct Costs By Segment	7,056	5,534	21,382	20,035
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total revenues	292,722	273,616	861,232	801,458
Gross Profit	243,505	231,245	716,120	675,119
Direct Costs By Segment	179,395	162,754	537,145	485,592
Income from operations	64,110	68,491	178,975	189,527
Depreciation, Depletion and Amortization, Nonproduction	$ 45,626	$ 39,372	$ 129,987	$ 118,597