CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended				12 Months Ended			36 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Operating Activities
Net income	$ 19,881	$ 20,750	$ 15,653	$ 12,222	$ 77,916	$ 55,789	$ 27,721
Adjustments to reconcile net income to cash provided by operating activities
Depreciation and amortization					4,624	4,435	4,209
Share-based compensation					4,520	3,124	4,267
Loss on sale of disposal of property, plant and equipment					17	48	94
Amortization of premium on investment securities					454	571	703
Deferred income taxes					1,598	(2,687)	(623)
Bad debt expense					3,638	1,058	151
Change in operating assets and liabilities:
Accounts receivable					(4,064)	(936)	664
Inventory					(9,883)	(18,658)	(1,017)
Income taxes, prepaid					(5,169)	2,272	(1,023)
Prepaid expenses and other current assets					(1,510)	(282)	(686)
Other assets					9	65	(1,876)
Accounts payable and accrued expenses					12,111	16,017	10,653
Net cash flow provided by operating activities					84,261	60,816	43,237
Investing Activities
Sale and maturities of investment securities					3,730	3,545	6,954
Purchase of investment securities							(6,956)
Sale of property and equipment						196	81
Purchase of property and equipment					(10,058)	(4,940)	(3,242)
Net cash flow used in investing activities					(6,328)	(1,199)	(3,163)
Financing Activities
Options exercised by executives and directors					278	547	568
Net shares repurchased for employee taxes					(14,092)	(720)	(2,540)
Cash dividends paid to stockholders					(35,396)	(23,160)	(15,390)
Stock repurchases					(33,114)	(29,995)
Net cash flow used in financing activities					(82,324)	(53,328)	(17,362)
Foreign currency impact					1	(2)	(71)
Increase (Decrease) in cash and cash equivalents					(4,390)	6,287	22,641
Cash and cash equivalents - beginning of the period		$ 81,364		$ 75,077	81,364	75,077	52,436	$ 52,436
Cash and cash equivalents - end of period	$ 76,974		$ 81,364		76,974	81,364	75,077	$ 76,974
Supplemental disclosure of cash flow information:
Income taxes paid					17,314	14,606	13,622
Dividends declared included in accounts payable					$ 13,719	$ 9,137	$ 6,105