Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Financial Statements, Captions [Line Items]
Revenue	$ 434,898	$ 464,712	$ 1,327,223	$ 1,305,650
Gross profit	222,074	222,891	672,539	620,944
Net earnings	$ 73,151	$ 63,529	$ 183,909	$ 157,513
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 0.53	$ 0.46	$ 1.33	$ 1.15
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 0.52	$ 0.46	$ 1.31	$ 1.13