CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 39,124	$ 56,093
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	9,819	9,088
Amortization of debt issuance costs	483	0
Stock-based compensation	16,882	13,692
Excess tax benefit from stock-based compensation	(3,150)	(1,684)
Deferred income taxes	2,807	1,769
Provision for excess and obsolete inventories	1,084	565
Other operating activities	3,037	(1,104)
Changes in assets and liabilities, net of effect of acquisition:
Accounts receivable, net	(2,825)	(1,632)
Inventory, net	(2,166)	(5,119)
Current and other assets	(2,190)	(2,931)
Accounts payable	9,016	8,158
Accrued liabilities	671	(7,771)
Income taxes	(6,144)	2,907
Cash provided by operating activities	66,448	72,031
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of investments	24,829	20,951
Proceeds from maturities of investments	40,405	81,275
Purchase of investments	(61,591)	(99,225)
Acquisition, net of cash acquired	0	(150)
Capital expenditures	(13,092)	(13,419)
Cash used for investing activities	(9,449)	(10,568)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(473,220)	(18,917)
Employees' tax withheld and paid for restricted stock and restricted stock units	(10,499)	(6,235)
Proceeds from issuances under stock-based compensation plans	9,071	11,424
Proceeds from revolving line of credit	155,749	0
Repayments of revolving line of credit	(190,249)	0
Proceeds from bonds issuance, net of issuance costs	488,401	0
Payment of cash dividends	(10,986)	(12,836)
Excess tax benefit from stock-based compensation	3,150	1,684
Cash used for financing activities	(28,583)	(24,880)
Effect of exchange rate changes on cash and cash equivalents	(430)	(1,058)
Net increase in cash and cash equivalents	27,986	35,525
Cash and cash equivalents at beginning of period	276,850	232,704
Cash and cash equivalents at end of period	$ 304,836	$ 268,229