Consolidated Statements of Cash Flows $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Cash flows from operating activities:
Net income	$ 108,839	$ 105,268	$ 65,203
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	14,867	12,311	16,101
(Gain) loss on disposal and sale of property and equipment, net	(259)	22	(3)
Amortization of premium on available-for-sale securities	729	1,353	1,976
(Gain) loss on deferred compensation plan investments	(3,806)	255	(2,531)
Deferred taxes, net	(577)	(843)	(15,238)
Stock-based compensation expense	78,699	60,607	52,617
Changes in operating assets and liabilities:
Accounts receivable	2,512	(18,079)	(3,785)
Inventories	8,865	(37,060)	(27,795)
Other assets	(10,204)	(1,075)	1,603
Accounts payable	3,048	871	3,077
Accrued compensation and related benefits	7,496	3,806	2,397
Accrued liabilities	7,449	7,092	10,852
Income tax liabilities	(1,355)	6,923	29,347
Net cash provided by operating activities	216,303	141,451	133,821
Cash flows from investing activities:
Purchases of property and equipment	(95,806)	(22,526)	(65,770)
Acquisition of in-place leases	(981)	0	0
Purchases of short-term investments	(212,562)	(99,199)	(140,531)
Proceeds from maturities and sales of short-term investments	135,801	109,131	77,502
Proceeds from sales of long-term investments	250	2,000	0
Proceeds from sales of property and equipment	9,268	0	0
Contributions to deferred compensation plan, net	(3,082)	(4,146)	(5,261)
Net cash used in investing activities	(167,112)	(14,740)	(134,060)
Cash flows from financing activities:
Property and equipment purchased on extended payment terms	(683)	(749)	(250)
Proceeds from common stock issued under the employee equity incentive plan	16,650	10,637	150
Proceeds from common stock issued under the employee stock purchase plan	3,277	3,028	2,701
Dividends and dividend equivalents paid	(67,294)	(47,475)	(33,926)
Net cash used in financing activities	(48,050)	(34,559)	(31,325)
Effect of change in exchange rates	(883)	(2,208)	1,625
Net increase (decrease) in cash, cash equivalents and restricted cash	258	89,944	(29,939)
Cash, cash equivalents and restricted cash, beginning of period	172,818	82,874	112,813
Cash, cash equivalents and restricted cash, end of period	173,076	172,818	82,874
Supplemental disclosures for cash flow information:
Cash paid for taxes	10,700	7,134	3,619
Non-cash investing and financing activities:
Liability accrued for property and equipment purchases	7,803	1,737	3,061
Liability accrued for dividends and dividend equivalents	$ 21,955	$ 16,319	$ 10,686