CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows From Operating Activities:
Net Income	$ 34,255	$ 36,593	$ 27,581
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	9,123	8,677	8,953
Deferred income taxes	(625)	(1,374)	(247)
Stock-based compensation	1,659	1,602	1,566
Impairment of investment	1,399	0	345
Net change in accrued interest, premiums, and discounts on investments	47	(195)	(37)
Other	(18)	49	0
Net Cash Provided By Used In Operating Activities Before Changes In Operating Capital, Total	45,840	45,352	38,161
Changes in operating assets and liabilities:
Accounts receivable	62	88	(546)
Inventories	(4,218)	(339)	756
Prepaid expenses and other current assets	(43)	(18)	(247)
Other non-current assets	(87)	75	(673)
Accounts payable and accrued liabilities	725	213	(324)
Accrued income and other taxes	(127)	336	81
Other non-current liabilities	1,084	1,330	195
Net Cash Provided by Operating Activities, Total	43,236	47,037	37,403
Cash Flows From Investing Activities:
Property, plant and equipment additions	(17,507)	(9,677)	(10,639)
Purchase of investments	(28,472)	(69,193)	(30,799)
Proceeds from sale of investments	0	0	210
Proceeds from maturities of investments	40,898	58,000	5,000
Net Cash Provided by (Used in) Investing Activities, Total	(5,081)	(20,870)	(36,228)
Cash Flows From Financing Activities:
Shares tendered for employees' withholding taxes on stock-based compensation	(90)	(7,735)	(1,112)
Purchase of treasury stock	0	0	(1,276)
Dividends paid	(9,448)	(8,318)	(7,111)
Net Cash Used in Financing Activities, Total	(9,538)	(16,053)	(9,499)
Net change in cash and cash equivalents	28,617	10,114	(8,324)
Cash and cash equivalents, beginning of year	30,136	20,022	28,346
Cash and cash equivalents, end of year	58,753	30,136	20,022
Cash paid for:
Income taxes, net of refunds	9,858	4,959	10,750
Non-cash financing activities:
Non-cash effect of stock option exercises	$ 0	$ 10,237	$ 0