Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Restructuring expenses													$ 4,854	$ 625	$ 1,431
Revenue	$ 448,463		$ 434,898		$ 452,707		$ 439,618		$ 494,784	$ 464,712	$ 434,124	$ 406,814	1,775,686	1,800,434	1,662,167
Gross profit	227,779		222,074		232,551		217,914	[1]	237,832	222,891	206,732	191,321	900,318	858,776	767,121
Net earnings	$ 98,516	[2]	$ 73,151	[2]	$ 71,563	[2]	$ 39,195	[2]	$ (50,290)	$ 63,529	$ 51,413	$ 42,571	$ 282,425	$ 107,223	$ 166,626
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 0.72		$ 0.53		$ 0.52		$ 0.28		$ (0.36)	$ 0.46	$ 0.38	$ 0.31	$ 2.05	$ 0.78	$ 1.22
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 0.71		$ 0.52		$ 0.51		$ 0.28		$ (0.36)	$ 0.46	$ 0.37	$ 0.31	$ 2.01	$ 0.77	$ 1.20

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