Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Statement of Cash Flows [Abstract]
Cash and cash equivalents at beginning of period	$ 688,087	$ 465,232
Cash flows from operating activities:
Net income	72,885	68,259
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	29,389	28,894
Amortization of debt discount and fees	292	350
Stock-based compensation	37,901	27,436
Gain on investments, net	(1,123)	(1,228)
Deferred income taxes	1,363	1,990
Provisions for losses on receivables	666	0
Other non-cash items	(43)	1,359
Changes in operating assets and liabilities, net of effect of acquired businesses:
Receivables	(10,988)	(22,475)
Inventories	2,105	6,000
Prepaid expenses and other	8,392	(3,777)
Other assets	8,152	(3,657)
Accounts payable and accrued liabilities	(46,956)	(46,159)
Deferred revenue	59,854	34,325
Other long-term liabilities	(4,242)	1,113
Net cash provided by operating activities	157,647	92,430
Cash flows from investing activities:
Proceeds from the sale of available-for-sale securities	0	107
Purchases of property, plant and equipment	(13,128)	(14,843)
Net cash used for investing activities	(13,128)	(14,736)
Cash flows from financing activities:
Proceeds from revolving credit facility	0	50,000
Payment on revolving credit facility	(40,000)	(50,000)
Payment of debt issuance costs	0	(793)
Proceeds from issuance of common stock	23,339	22,715
Stock received for payment of employee taxes on vesting of restricted stock	(26,515)	(22,470)
Payments for repurchases of common stock	(50,013)	0
Change in book overdraft	(3,867)	0
Net cash used for financing activities	(97,056)	(548)
Effect of exchange rate changes on cash and cash equivalents	11,418	1,750
Increase in cash and cash equivalents	58,881	78,896
Cash and cash equivalents at end of period	746,968	544,128
Supplemental cash flow information:
Cash paid for interest	2,716	2,219
Cash paid for taxes, net	$ 6,025	$ 9,767