Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Income	$ 26,335	$ 40,418	$ 41,281
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	19,447	19,506	19,001
Provision for doubtful accounts	34	185	(237)
Provision for warranty and returns	(360)	671	220
Stock compensation	9,592	5,434	5,563
Loss (gain) on disposal of property and equipment	8	(36)	212
Bond premium amortization	2,188	2,715	2,585
Cash provided (used) by changes in operating assets and liabilities
Accounts receivable	4,912	3,556	(5,395)
Inventories	(3,836)	2,319	4,573
Prepaid expenses and other assets	1,970	(383)	(415)
Accounts payable	(621)	(31)	(1,536)
Accrued liabilities	2,344	(2,215)	1,199
Income taxes, including excess tax benefits and deferred income taxes	(1,373)	(6,413)	(780)
Net cash provided by operating activities	60,640	65,726	66,271
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(16,604)	(18,415)	(19,160)
Proceeds from Sale of Assets	5	49	10
Intangible asset additions	(989)	(1,080)	(1,145)
Purchases of investment securities	(93,588)	(86,022)	(98,876)
Proceeds from sale of investment securities	89,426	92,348	77,798
Net cash used by investing activities	(21,750)	(13,120)	(41,373)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of stock options	16,998	18,004	14,844
Proceeds from employee stock purchase plan	2,485	2,457	2,220
Excess Tax Benefit from Share-based Compensation, Financing Activities	5,700	6,966	4,567
Purchase of treasury stock	(5,836)	(3,033)	0
Net cash provided by financing activities	19,347	24,394	21,631
Effect of exchange rate changes on cash	(8,447)	2,122	781
NET INCREASE IN CASH AND CASH EQUIVALENTS	49,790	79,122	47,310
CASH AND CASH EQUIVALENTS, beginning of period	226,022	146,900	99,590
CASH AND CASH EQUIVALENTS, end of period	275,812	226,022	146,900
SUPPLEMENTAL DISCLSOURE OF CASH FLOW INFORMATION
Cash paid during the year for income taxes	8,668	12,172	16,741
NON-CASH INVESTING ACTIVITIES
Accrued liabilities for property and equipment	$ 789	$ 212	$ 427