Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Cash flows from operating activities:
Net income	$ 105,268	$ 65,203	$ 52,720
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization of intangible assets	12,311	16,101	14,674
(Gain) loss on sales or write-off of property and equipment	22	(3)	57
Amortization of premium on available-for-sale securities	1,353	1,976	1,019
(Gain) loss on deferred compensation plan investments	255	(2,531)	(1,257)
Deferred taxes, net	(843)	(15,238)	(5)
Excess tax benefits from equity awards			(1,465)
Stock-based compensation expense	60,607	52,617	44,989
Changes in operating assets and liabilities:
Accounts receivable	(18,079)	(3,785)	(3,421)
Inventories	(37,060)	(27,795)	(8,323)
Other assets	(1,075)	1,603	(11,021)
Accounts payable	871	3,077	5,483
Accrued compensation and related benefits	3,806	2,397	3,136
Accrued liabilities	7,092	10,852	8,035
Income tax liabilities	6,923	29,347	3,165
Net cash provided by operating activities	141,451	133,821	107,786
Cash flows from investing activities:
Property and equipment purchases	(22,526)	(65,770)	(37,112)
Purchases of short-term investments	(99,199)	(140,531)	(236,912)
Proceeds from maturities and sales of short-term investments	109,131	77,502	223,344
Proceeds from sales of long-term investments	2,000
Contributions to deferred compensation plan, net	(4,146)	(5,261)	(5,046)
Net cash used in investing activities	(14,740)	(134,060)	(55,726)
Cash flows from financing activities:
Property and equipment purchased on extended payment terms	(749)	(250)	(300)
Proceeds from exercise of stock options	59	150	1,344
Proceeds from vesting of restricted stock units	10,578
Proceeds from shares issued under the employee stock purchase plan	3,028	2,701	2,463
Dividends and dividend equivalents paid	(47,475)	(33,926)	(33,099)
Excess tax benefits from equity awards			1,465
Net cash used in financing activities	(34,559)	(31,325)	(28,127)
Effect of change in exchange rates	(2,208)	1,625	(2,093)
Net increase (decrease) in cash, cash equivalents and restricted cash	89,944	(29,939)	21,840
Cash, cash equivalents and restricted cash, beginning of period	82,874	112,813	90,973
Cash, cash equivalents and restricted cash, end of period	172,818	82,874	112,813
Supplemental disclosures for cash flow information:
Cash paid for taxes and interest	7,134	3,619	1,234
Non-cash investing and financing activities:
Liability accrued for property and equipment purchases	1,737	3,061	787
Liability accrued for dividends and dividend equivalents	$ 16,319	$ 10,686	$ 10,416