Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Cash flows from operating activities:
Net income	$ 52,720	$ 35,172	$ 35,495
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of intangible assets	14,674	13,783	13,130
(Gain) loss on sales or write-off of property and equipment	57	(339)
Amortization of premium on available-for-sale investments, net	1,019	463	237
(Gain) loss on employee deferred compensation plan investments	(1,257)	133	(141)
Change in fair value of contingent consideration		(2,507)
Deferred taxes, net	(5)	42	17
Excess tax benefits from equity awards	(1,465)	(5,928)	(10)
Stock-based compensation expense	44,989	41,563	33,454
Changes in operating assets and liabilities, net of effects of an acquisition:
Accounts receivable	(3,421)	(5,201)	(1,870)
Inventories	(8,323)	(22,210)	(1,142)
Other assets	(11,021)	(390)	(2,029)
Accounts payable	5,483	147	1,632
Accrued liabilities	8,035	9,942	(3,102)
Income tax liabilities	3,165	3,998	(248)
Accrued compensation and related benefits	3,136	1,068	(1,290)
Net cash provided by operating activities	107,786	69,736	74,133
Cash flows from investing activities:
Property and equipment purchases	(37,112)	(16,024)	(9,511)
Proceeds from sales of property and equipment		340
Purchases of short-term investments	(236,912)	(223,018)	(136,872)
Proceeds from maturities and sales of short-term investments	223,344	189,549	149,291
Proceeds from sales of long-term investment			4,650
Contributions to employee deferred compensation plan, net	(5,046)	(8,044)	(5,335)
Cash paid for an acquisition, net of cash acquired			(11,590)
Net cash used in investing activities	(55,726)	(57,197)	(9,367)
Cash flows from financing activities:
Property and equipment purchased on extended payment terms	(300)	(300)	(400)
Proceeds from exercise of stock options	1,344	7,744	11,941
Proceeds from shares issued under the employee stock purchase plan	2,463	2,227	2,078
Repurchases of common shares		(32,286)	(41,198)
Dividends and dividend equivalents paid	(33,099)	(29,965)	(11,658)
Excess tax benefits from equity awards	1,465	5,928	10
Net cash used in financing activities	(28,127)	(46,652)	(39,227)
Effect of change in exchange rates	(2,090)	(1,293)	(486)
Net increase (decrease) in cash and cash equivalents	21,843	(35,406)	25,053
Cash and cash equivalents, beginning of period	90,860	126,266	101,213
Cash and cash equivalents, end of period	112,703	90,860	126,266
Supplemental disclosures for cash flow information:
Cash paid for taxes and interest	1,234	3,322	1,235
Supplemental disclosures of non-cash investing and financing activities:
Liability accrued for property and equipment purchases	787	2,184	1,487
Liability accrued for dividends and dividend equivalents	10,416	10,109	6,660
Sensima [Member]
Supplemental disclosures of non-cash investing and financing activities:
Fair value of contingent consideration related to an acquisition			$ 2,507