Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Revenue	$ 439,618	$ 406,814
Gross profit	217,914	191,321
Net earnings	$ 39,195	$ 42,571
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 0.28	$ 0.31
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 0.28	$ 0.31