Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Financial Statements, Captions [Line Items]
Revenue	$ 452,707	$ 434,124	$ 892,325	$ 840,938
Gross profit	232,551	206,732	450,465	398,053
Net earnings	$ 71,563	$ 51,413	$ 110,758	$ 93,984
Basic earnings per share:
Basic earnings per share (in dollars per share)	$ 0.52	$ 0.38	$ 0.80	$ 0.69
Diluted earnings per share:
Diluted earnings per share (in dollars per share)	$ 0.51	$ 0.37	$ 0.79	$ 0.68