Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Income	$ 40,418	$ 41,281	$ 44,669
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	19,506	19,001	18,294
Provision for doubtful accounts	185	(237)	648
Provision for warranty and returns	671	220	0
Stock compensation	5,434	5,563	4,016
Loss (gain) on disposal of property and equipment	(36)	212	(42)
Gain on sale of assets	0	0	(14,242)
Bond premium amortization	2,715	2,585	1,294
Cash provided (used) by changes in operating assets and liabilities
Accounts receivable	3,556	(5,395)	6,232
Inventories	2,319	4,573	3,170
Prepaid expenses and other assets	(383)	(415)	(920)
Accounts payable	(31)	(1,536)	2,673
Accrued liabilities	(2,215)	1,199	1,684
Deferred revenue	0	0	(254)
Income taxes, including excess tax benefits and deferred income taxes	(6,413)	(780)	(2,735)
Net cash provided by operating activities	65,726	66,271	64,487
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(18,415)	(19,160)	(15,824)
Proceeds from Sale of Assets	49	10	16,201
Proceeds from insurance	0	0	2,781
Intangible asset additions	(1,080)	(1,145)	0
Purchases of investment securities	(86,022)	(98,876)	(90,502)
Proceeds from sale of investment securities	92,348	77,798	41,610
Net cash provided (used) by investing activities	(13,120)	(41,373)	(45,734)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of stock options	18,004	14,844	7,974
Proceeds from employee stock purchase plan	2,457	2,220	1,828
Tax Benefit from Stock Options Exercised	6,966	4,567	4,288
Purchase of treasury stock	(3,033)	0	(11,956)
Net cash provided (used) by financing activities	24,394	21,631	2,134
Effect of exchange rate changes on cash	2,122	781	(147)
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	79,122	47,310	20,740
CASH AND CASH EQUIVALENTS, beginning of period	146,900	99,590	78,850
CASH AND CASH EQUIVALENTS, end of period	226,022	146,900	99,590
SUPPLEMENTAL DISCLSOURE OF CASH FLOW INFORMATION
Cash paid during the year for income taxes	12,172	16,741	20,110
NON-CASH INVESTING ACTIVITIES
Accrued liabilities for property and equipment	$ 212	$ 427	$ 418