Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)	Mar. 31, 2016 USD ($)
Cash flows from operating activities:
Net income (loss)	$ 79,812	$ 33,291	$ (28,369)
Adjustments to reconcile net income (loss) to cash provided by operating activities, net of the effects of acquisitions:
Depreciation and amortization	153,503	160,863	140,071
Loss on disposal of fixed assets	481	271	134
Deal related compensation expense and accretion charges	153	153	6,728
Share-based compensation expense associated with equity awards	47,317	39,189	28,351
Deferred income taxes	(127,784)	(11,008)	(42,121)
Other (gains) losses	18	(111)	(279)
Changes in assets and liabilities
Accounts receivable and unbilled costs	84,952	(48,080)	(23,259)
Due from related party	443	25,055	(18,483)
Inventories	1,006	12,456	5,523
Prepaid expenses and other assets	20,147	(24,751)	(29,481)
Accounts payable	(8,929)	405	2,334
Accrued compensation and other expenses	(17,718)	6,785	33,250
Due to related party	(75)	(2,792)	(6,743)
Income taxes payable	(2,734)	1,963	3,910
Deferred revenue	(8,138)	33,075	25,645
Net cash provided by operating activities	222,454	226,764	97,211
Cash flows from investing activities:
Purchase of marketable securities	(114,178)	(199,841)	(100,278)
Proceeds from maturity of marketable securities	196,041	181,321	118,881
Purchase of fixed assets	(15,913)	(29,696)	(24,783)
Purchase of intangible assets	(544)	(1,031)	(3,962)
Acquisition of businesses, net of cash acquired	(8,334)	(4,606)	27,700
(Increase) decrease in deposits	(330)	129	(150)
Contingent purchase consideration	523	660	0
Collection of contingently returnable consideration	0	12,864	9,306
Capitalized software development costs	(137)	(1,421)	(1,625)
Net cash provided by (used in) investing activities	57,128	(41,621)	25,089
Cash flows from financing activities:
Issuance of common stock under stock plans	1	2	1
Payment of contingent consideration	(660)	0	0
Treasury stock repurchases, including accelerated share repurchases	(501,324)	(79,996)	(302,784)
Tax withholding on restricted stock units	(13,598)	(9,559)	(9,066)
Proceeds from issuance of long-term debt, net of issuance costs	294,619	0	294,623
Net cash used in financing activities	(220,962)	(89,553)	(17,226)
Effect of exchange rate changes on cash and cash equivalents	6,385	(761)	744
Net increase in cash and cash equivalents	65,005	94,829	105,818
Cash and cash equivalents, beginning of year	305,726	210,897	105,079
Cash and cash equivalents, end of year	370,731	305,726	210,897
Supplemental disclosures of cash flow information:
Cash paid for interest	9,604	6,442	3,807
Cash paid for income taxes	18,216	49,290	50,658
Non-cash transactions:
Transfers of inventory to fixed assets	5,556	4,928	1,229
Additions to property, plant and equipment included in accounts payable	1,379	1,241	(1,065)
Debt issuance costs settled through the issuance of additional debt	0	0	5,377
Issuance of common stock under employee stock purchase plans	17,849	15,697	10,560
Contingent consideration related to acquisition, included in accrued other	523	660	0
Tenant improvement allowance	2,104	0	0
Purchase consideration
Non-cash transactions:
Noncash business transaction	0	0	2,276,256
Contingently returnable consideration
Non-cash transactions:
Noncash business transaction	$ 0	$ 0	$ 29,355