Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes Paid	$ 32,090	$ 35,149	$ 40,273
Cash flows from operating activities:
Net Income	19,436	75,851	48,584
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	26,094	31,993	35,850
Purchase premium amortization/discount accretion on investments, net	46	167	(57)
Non-cash stock-based compensation	22,147	18,949	16,825
Income tax impact associated with stock option exercises	0	2,454	(2,233)
Deferred income taxes	21,836	(2,723)	(710)
Changes in assets and liabilities, net of effect of acquisitions:
Accounts receivable	(98,959)	(23,206)	(14,952)
Inventories	1,967	(34,744)	9,765
Prepaid expenses and other assets	5,161	5,932	560
Accounts payable	(784)	21,327	(14,990)
Accrued employee compensation	(5,345)	5,228	6,280
Other accrued liabilities	57,650	6,907	29,987
Deferred revenue	19,982	6,176	(2,496)
Income taxes payable	18,293	3,870	(1,263)
Net cash provided by operating activities	87,524	118,181	111,150
Cash flows from investing activities:
Purchases of short-term investments	(136,556)	(144,271)	(110,316)
Proceeds from maturities of short-term investments	135,549	115,291	130,273
Purchases of property and equipment	(13,674)	(10,972)	(14,000)
Purchases of cost method investments	(4,400)	0	0
Payments made in connection with business acquisitions, net of cash acquired	(737)	(8,807)	0
Net cash provided by (used in) investing activities	(19,818)	(48,759)	5,957
Cash flows from financing activities:
Repurchases of common stock	(113,161)	(38,252)	(117,680)
Restricted stock unit withholdings	(6,415)	(4,686)	(2,629)
Proceeds from exercise of stock options	9,508	28,147	40,928
Proceeds from issuance of common stock under employee stock purchase plan	4,764	3,892	2,985
Net cash used in financing activities	(105,304)	(10,899)	(76,396)
Net increase (decrease) in cash and cash equivalents	(37,598)	58,523	40,711
Cash and cash equivalents, at beginning of period	240,468	181,945	141,234
Cash and cash equivalents, at end of period	$ 202,870	$ 240,468	$ 181,945