CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 17,502,000	$ 19,102,000
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	5,574,000	5,209,000
Deferred income taxes	503,000	1,408,000
Stock-based compensation	991,000	980,000
Net change in unrealized gains and losses on investments	933,000	(364,000)
Net change in accrued interest, premiums, and discounts on investments	(66,000)	173,000
Other	22,000	(6,000)
Net Cash Provided By Used In Operating Activities Before Changes In Operating Capital, Total	25,459,000	26,502,000
Changes in operating assets and liabilities:
Accounts receivable	(3,558,000)	(3,354,000)
Inventories	(3,712,000)	(1,018,000)
Prepaid expenses	(681,000)	311,000
Other non-current assets	(254,000)	57,000
Accounts payable and accrued liabilities	518,000	542,000
Accrued income and other taxes	3,651,000	180,000
Other non-current liabilities	(2,000,000)	912,000
Net Cash Provided by Operating Activities, Total	19,423,000	24,132,000
Cash flows from investing activities:
Property, plant and equipment additions	(8,800,000)	(9,977,000)
Purchase of investments	(30,444,000)	(45,843,000)
Proceeds from sale of investments	896,000	0
Proceeds from maturities of investments	20,774,000	28,121,000
Net Cash Provided by Investing Activities, Total	(17,574,000)	(27,699,000)
Cash flows from financing activities:
Purchase of treasury stock	17,037,000	0
Shares tendered for employees' withholding taxes on stock-based compensation	(55,000)	(579,000)
Dividends paid	(5,706,000)	(5,005,000)
Net Cash Provided by Financing Activities, Total	(22,798,000)	(5,584,000)
Net change in cash and cash equivalents	(20,949,000)	(9,151,000)
Cash and cash equivalents at beginning of period	45,048,000	58,753,000
Cash and cash equivalents at end of the period	24,099,000	49,602,000
Income taxes	$ 199,000	$ 2,104,000