CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended				12 Months Ended			24 Months Ended
	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019
Operating Activities
Net income	$ 27,994	$ 18,477	$ 19,881	$ 20,750	$ 102,859	$ 77,916	$ 55,789
Adjustments to reconcile net income to cash provided by operating activities
Depreciation and amortization					7,270	7,248	4,435
Share-based compensation					6,796	4,520	3,124
Loss on sale of disposal of property, plant and equipment					212	17	48
Bad debt expense					556	3,638	1,058
Amortization of premium on investment securities					320	454	571
Deferred income taxes					601	1,598	(2,687)
Change in operating assets and liabilities:
Accounts receivable					297	(4,064)	(936)
Inventories					(4,621)	(9,883)	(18,658)
Income taxes, prepaid					5,169	(5,169)	2,272
Prepaid expenses and other current assets					233	(1,510)	(282)
Other assets					(2,506)	(2,615)	65
Accounts payable and accrued expenses					28,010	12,111	16,017
Net cash flow provided by operating activities					145,196	84,261	60,816
Investing Activities
Sale and maturities of investment securities					4,605	3,730	3,545
Sale of property and equipment							196
Purchase of property and equipment					(5,887)	(10,058)	(4,940)
Net cash flow used in investing activities					(1,282)	(6,328)	(1,199)
Financing Activities
Options exercised by executives and directors					1,597	278	547
Net shares repurchased for employee taxes					(551)	(14,092)	(720)
Cash dividends paid to stockholders					(53,190)	(35,396)	(23,160)
Stock repurchases					(5,000)	(33,114)	(29,995)
Net cash flow used in financing activities					(57,144)	(82,324)	(53,328)
Foreign currency impact					(21)	1	(2)
Increase (Decrease) in cash and cash equivalents					86,749	(4,390)	6,287
Cash and cash equivalents - beginning of the period		$ 76,974		$ 81,364	76,974	81,364	75,077	$ 75,077
Cash and cash equivalents - end of the period	$ 163,723		$ 76,974		163,723	76,974	81,364	$ 76,974
Supplemental disclosure of cash flow information:
Income taxes paid					24,636	17,314	14,606
Dividends declared included in accounts payable					$ 13,831	$ 13,719	$ 9,137