CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Operating activities:
Net income	$ 75,323	$ 37,217
Adjustments required to reconcile net income to net cash provided by operating activities:
Depreciation expense	8,100	4,488
Bad debt expense	(8)	(12)
Stock-based compensation	29,170	24,521
Write-down of inventory and other assets	3,212	2,059
Excess tax benefit from stock-based awards		(4,595)
Deferred tax provision	34,740	18,817
Change in fair value of contingent consideration	1,270	612
Changes in assets and liabilities:
Accounts receivable	(10,342)	(7,555)
Inventories	(11,974)	(8,615)
Prepaid expenses and other assets	(1,033)	(3,923)
Accounts payable	2,595	3,542
Accrued expenses and other liabilities	3,874	11,040
Deferred revenue	1,220	265
Net cash provided by operating activities	136,147	77,861
Investing activities:
Purchases of marketable securities	(209,834)	(177,591)
Proceeds from the sale and maturity of marketable securities	148,095	144,670
Purchase of other investment	(6,400)	(149)
Purchases of property and equipment	(44,168)	(24,039)
Net cash used for investing activities	(112,307)	(57,109)
Financing activities:
Proceeds from the exercise of stock options	7,626	8,265
Excess tax benefit from stock-based awards		4,595
Taxes paid related to net share settlement of vesting of stock awards	(19,860)	(19,898)
Proceeds from the issuance of stock under employee stock purchase plan	1,063	769
Principal payments on capital lease obligation	(517)	(264)
Net cash used for financing activities	(11,688)	(6,533)
Effect of exchange rate changes on cash	(690)	(1,381)
Net increase in cash and cash equivalents	11,462	12,838
Cash and cash equivalents at beginning of period	39,040	48,231
Cash and cash equivalents at end of period	50,502	61,069
Supplemental disclosure of cash flow information:
Cash paid for income taxes	845	735
Cash paid for interest on capital lease obligation	302	223
Supplemental disclosure of non-cash investing and financing activities:
Property and equipment under capital lease obligation		16,784
Property and equipment in accounts payable and accrued expenses	$ 3,836	$ 3,717