CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended			12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (113,971)	$ (10,723)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depreciation and amortization	142,763	15,894
Amortization of debt issuance costs	3,188	1,087
Stock-based compensation	30,709	26,047
Deferred income taxes	(39,987)	10,490
Provision for excess and obsolete inventories	4,881	2,013
Restructuring and related charges (credits)	20,711	2,438
Cash payments for restructuring charges	(11,222)	(2,911)
Other operating activities	9,070	(645)
Changes in assets and liabilities, net of acquisition:
Accounts receivable, net	(35,938)	(3,153)
Inventory, net	11,018	(9,577)
Current and other assets	30,456	(3,066)
Accounts payable	16,519	2,783
Accrued liabilities	72,677	(15,695)
Income taxes	(21,631)	66,387
Cash provided by operating activities	119,243	81,369
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of investments	125,799	54,411
Proceeds from maturities of investments	131,017	146,989
Purchase of investments	(698)	(232,840)
Cash paid for acquisition, net of cash acquired	(1,642,241)	0
Capital expenditures	(16,148)	(9,403)
Cash used for investing activities	(1,402,271)	(40,843)
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(4,780)	(52,915)
Employees' tax withheld and paid for restricted stock and restricted stock units	(13,863)	(11,186)	$ (11,186)
Proceeds from issuances under stock-based compensation plans	14,925	13,446
Proceeds from revolving line of credit			8,000	$ 0
Repayments of revolving line of credit			$ (8,000)	0
Proceeds from debt issuance, net	1,244,713	0
Payment of cash dividends	(16,953)	(15,008)
Cash (used for) provided by financing activities	1,224,042	(65,663)
Effect of exchange rate changes on cash and cash equivalents	(3,519)	3,460
Net increase (decrease) in cash and cash equivalents	(62,505)	(21,677)
Cash and cash equivalents at beginning of period	390,661	301,970		301,970
Cash and cash equivalents at end of period	328,156	280,293		$ 390,661
SUPPLEMENTAL NON-CASH DISCLOSURES
Cash paid for income taxes	30,902	8,127
Cash paid for interest	$ 54,386	$ 27,781