Note 2 - Revenue Recognition - Impact of Topic 606 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017		Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Accounts receivable	$ 53,460			$ 53,460		$ 38,037
Inventories	128,909			128,909		99,281
Other current assets	13,974			13,974		12,762
Deferred tax assets, net	15,791			15,791		15,917
Total assets	719,952			719,952		652,569
Accrued liabilities	33,033			33,033		27,507
Retained earnings	162,859			162,859		143,608
Total liabilities and stockholders' equity	719,952			719,952		$ 652,569
Revenue	139,761	$ 112,198	[1]	268,911	$ 212,560
Cost of revenue	62,197	50,773		119,852	96,293
Gross profit	77,564	61,425		149,059	116,267
Income from operations	24,882	14,970		46,918	28,540
Income before income taxes	27,114	16,207		49,591	31,158
Income tax provision	2,908	1,193		3,529	1,668
Net income	$ 24,206	$ 15,014		$ 46,062	$ 29,490
Net income per share - diluted (in dollars per share)	$ 0.55	$ 0.35		$ 1.04	$ 0.68
Comprehensive income	$ 17,459	$ 16,341		$ 42,544	$ 32,325
Accounts receivable				(16,325)	(7,729)
Inventories				(29,602)	(21,158)
Other assets				(983)	(1,167)
Accrued liabilities				539	3,177
Income tax liabilities				1,546	$ 78
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Accounts receivable	55,016			55,016
Inventories	128,938			128,938
Other current assets	12,927			12,927
Deferred tax assets, net	15,892			15,892
Total assets	720,591			720,591
Accrued liabilities	34,178			34,178
Retained earnings	162,353			162,353
Total liabilities and stockholders' equity	720,591			720,591
Revenue	139,758			268,717
Cost of revenue	62,234			119,818
Gross profit	77,524			148,899
Income from operations	24,842			46,758
Income before income taxes	27,074			49,431
Income tax provision	2,900			3,496
Net income	$ 24,174			$ 45,935
Net income per share - diluted (in dollars per share)	$ 0.54			$ 1.04
Comprehensive income	$ 17,427			$ 42,417
Accounts receivable				(16,980)
Inventories				(29,631)
Other assets				(27)
Accrued liabilities				428
Income tax liabilities				1,512
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Accounts receivable	(1,556)			(1,556)
Inventories	(29)			(29)
Other current assets	1,047			1,047
Deferred tax assets, net	(101)			(101)
Total assets	(639)			(639)
Accrued liabilities	(1,145)			(1,145)
Retained earnings	506			506
Total liabilities and stockholders' equity	(639)			(639)
Revenue	3			194
Cost of revenue	(37)			34
Gross profit	40			160
Income from operations	40			160
Income before income taxes	40			160
Income tax provision	8			33
Net income	$ 32			$ 127
Net income per share - diluted (in dollars per share)	$ 0.01
Comprehensive income	$ 32			$ 127
Accounts receivable				655
Inventories				29
Other assets				(956)
Accrued liabilities				111
Income tax liabilities				$ 34

[1] 2017 amounts have not been adjusted under the modified retrospective method.