Quarterly Results (unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 284,713	$ 359,371	$ 376,315	$ 366,121	$ 278,663	$ 302,395	$ 332,658	$ 297,504	$ 1,386,520	$ 1,211,220	$ 1,143,492
Gross Profit	61,377	94,566	96,754	86,059	61,500	87,380	91,210	71,955	338,756	312,045	231,617
Earnings Before Income Taxes	48,725	51,388	92,319	79,530	54,181	83,689	89,373	67,276	271,962	294,519	219,252
Net Earnings	$ 37,008	$ 101,380	$ 63,362	$ 54,882	$ 36,251	$ 56,387	$ 60,237	$ 45,344	$ 256,632	$ 198,219	$ 152,592
Diluted Earnings Per Share	$ 0.76	$ 2.08	$ 1.31	$ 1.13	$ 0.75	$ 1.17	$ 1.25	$ 0.93	$ 5.28	$ 4.10	$ 3.05