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Reportable Segments - Operations of Segments (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenue	$ 336,230	$ 345,558	$ 338,861	$ 326,738	$ 330,377	$ 326,584	$ 329,535	$ 317,441	$ 1,347,387	$ 1,303,937	$ 1,253,646
Gross profit	$ 98,025	$ 102,811	$ 101,026	$ 93,176	$ 97,713	$ 96,045	$ 100,220	$ 92,509	395,038	386,487	375,597
Operating and other expenses									323,642	318,607	320,679
Income from continuing operations, before income taxes									71,396	67,880	54,918
Tech
Segment Reporting Information [Line Items]
Revenue									1,057,859	990,089	907,511
Gross profit									292,980	277,388	257,118
FA
Segment Reporting Information [Line Items]
Revenue									289,528	313,848	346,135
Gross profit									$ 102,058	$ 109,099	$ 118,479