CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities:
Net income	$ 140,193	$ 61,877
Adjustments required to reconcile net income to net cash provided by operating activities:
Depreciation expense	6,347	5,320
Bad debt expense (recovery)	467	(54)
Stock-based compensation	28,179	17,938
Write-down of inventory and other	1,733	2,528
Accretion on marketable securities	(848)
Deferred tax provision	(45,676)	3,073
Change in fair value of contingent consideration	3	682
Changes in assets and liabilities:
Accounts receivable	(5,131)	(2,824)
Inventories	(16,750)	(5,363)
Prepaid expenses and other assets	(1,987)	(869)
Accounts payable	761	299
Accrued expenses and other liabilities	826	(3,174)
Deferred revenue	(926)	18
Net cash provided by operating activities	107,191	79,451
Investing activities:
Purchases of marketable securities	(112,956)	(131,934)
Proceeds from the sale and maturity of marketable securities	136,844	95,416
Purchase of other assets	(11,426)	(6,400)
Purchases of property and equipment	(27,345)	(17,675)
Net cash used for investing activities	(14,883)	(60,593)
Financing activities:
Proceeds from the exercise of stock options	10,613	5,257
Taxes paid related to net share settlement of vesting of stock awards	(69,666)	(19,237)
Proceeds from the issuance of stock under employee stock purchase plan	1,375	1,063
Principal payments on capital lease obligation		(377)
Net cash used for financing activities	(57,678)	(13,294)
Effect of exchange rate changes on cash	(1,223)	(68)
Net increase in cash and cash equivalents	33,407	5,496
Cash and cash equivalents at beginning of period	42,975	39,040
Cash and cash equivalents at end of period	76,382	44,536
Supplemental disclosure of cash flow information:
Cash paid for income taxes	3,530	584
Cash paid for interest on capital lease obligation		259
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment in accounts payable and accrued expenses	$ 1,399	$ 897