Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 7,463,841	$ 6,704,037	$ 6,167,600
Operating costs and expenses:
Cost of revenue	3,379,180	3,100,466	2,866,268
Billable expenses	2,298,413	2,004,664	1,861,312
General and administrative expenses	1,035,965	927,938	855,541
Depreciation and amortization	81,081	68,575	64,756
Total operating costs and expenses	6,794,639	6,101,643	5,647,877
Operating income	669,202	602,394	519,723
Interest expense	(96,960)	(89,517)	(82,269)
Other income (expense), net	7,192	2,526	(7,418)
Income before income taxes	579,434	515,403	430,036
Income tax expense	96,831	96,874	128,344
Net income	$ 482,603	$ 418,529	$ 301,692
Earnings per common share (Note 3):
Basic (in dollars per share)	$ 3.43	$ 2.94	$ 2.05
Diluted (in dollars per share)	$ 3.41	$ 2.91	$ 2.03