Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
CASH FLOWS FROM OPERATING ACTIVITIES:
Net Income	$ 63,084	$ 44,985	$ 26,335
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	19,050	18,073	19,447
Provision for doubtful accounts	0	54	34
Provision for warranty and returns	559	52	(360)
Stock compensation	15,242	12,827	9,592
Loss (gain) on disposal of property and equipment	59	(1,106)	8
Bond premium amortization	1,355	1,670	2,188
Impairment of assets held for sale	728	4,139	0
Business Combination, Bargain Purchase, Gain Recognized, Amount	(1,456)	0	0
Other	75	0	0
Cash provided (used) by changes in operating assets and liabilities
Accounts receivable	744	(20,515)	4,912
Inventories	(5,501)	(8,337)	(3,836)
Prepaid expenses and other assets	(3,028)	(1,832)	1,970
Accounts payable	(463)	3,118	(621)
Accrued liabilities	(1,221)	9,454	2,344
Income taxes, including excess tax benefits and deferred income taxes	714	1,613	4,327
Net cash provided by operating activities	89,941	64,195	66,340
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(23,361)	(12,984)	(16,604)
Proceeds from sale of assets acquired in a business combination	0	3,592	5
Proceeds from the disposal of assets held for sale	3,268	0	0
Intangible asset additions	(1,192)	(951)	(989)
Business acquisitions, net of cash acquired	(2,584)	(56,786)	0
Proceeds from sale of business	0	28,970	0
Purchases of investment securities	(118,384)	(56,137)	(93,588)
Proceeds from sale of investment securities	158,534	83,054	89,426
Net cash used by investing activities	16,281	(11,242)	(21,750)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from exercise of stock options	17,346	15,042	16,998
Proceeds from employee stock purchase plan	2,361	2,162	2,485
Purchase of treasury stock	(17,235)	(1,523)	(5,836)
Net cash provided by financing activities	2,472	15,681	13,647
Effect of exchange rate changes on cash	224	(8,282)	(8,447)
NET INCREASE IN CASH AND CASH EQUIVALENTS	108,918	60,352	49,790
CASH AND CASH EQUIVALENTS, beginning of period	336,164	275,812	226,022
CASH AND CASH EQUIVALENTS, end of period	445,082	336,164	275,812
SUPPLEMENTAL DISCLSOURE OF CASH FLOW INFORMATION
Cash paid during the year for income taxes	21,101	22,998	8,668
NON-CASH INVESTING ACTIVITIES
Accrued liabilities for property and equipment	1,566	182	$ 789
Fair value of assets acquired	3,306	60,693
Liabilities assumed	$ 734	$ 3,907