Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income (loss)	$ (15,345)	$ 44,949	$ 32,199
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	65,647	55,081	40,124
Deferred taxes	8,753	(11,091)	(7,997)
Tax benefit from employee stock plans			5,369
Provision for bad debts and sales-related allowances	12,416	10,678	7,536
Provision for inventory obsolescence	6,312	5,716	7,147
Stock-based compensation, net of cash settlements	26,532	31,726	33,741
Contingent consideration payments related to businesses acquired	(5,906)
Non-cash accretion of interest expense on convertible notes and imputed financing obligation	14,981	13,489	12,957
Other non-cash charges and credits	12,536	5,443	3,844
Changes in operating assets and liabilities, net of effect of acquired businesses:
Accounts receivable	(29,189)	(31,221)	(34,355)
Inventories	(24,398)	4,510	(6,758)
Other current assets	(9,218)	(6,498)	(14,863)
Accounts payable and accrued liabilities	(6,235)	651	(6,371)
Income taxes receivable/payable, net	(5,591)	(2,429)	(4,216)
Net cash provided by operating activities	51,295	121,004	68,357
Cash flows from investing activities:
Purchases of short-term investments	(87,623)	(216,349)	(328,911)
Proceeds from sales and maturities of short-term investments	233,633	252,856	311,508
Purchases of restricted cash equivalents and investments	(26,274)	(6,252)
Purchases, net of proceeds from sales, of property and equipment	(13,754)	(22,373)	(18,449)
Businesses and technology purchased, net of cash acquired and disposition	(29,559)	(19,932)	(74,766)
Net cash provided by (used for) investing activities	76,423	(12,050)	(110,618)
Cash flows from financing activities:
Proceeds from issuance of common stock	12,074	11,100	11,450
Purchases of treasury stock and net share settlements	(101,844)	(83,292)	(76,447)
Repayment of debt assumed through business acquisitions and debt issuance costs	(11,094)	(8,803)	(22,592)
Contingent consideration payments related to businesses acquired	(25,018)	(28,111)	(4,093)
Net cash used for financing activities	(125,882)	(109,106)	(91,682)
Effect of foreign exchange rate changes on cash and cash equivalents	4,196	374	(99)
Increase (decrease) in cash and cash equivalents	6,032	222	(134,042)
Cash and cash equivalents at beginning of year	164,313	164,091	298,133
Cash and cash equivalents at end of year	$ 170,345	$ 164,313	$ 164,091