CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash Flows From Operating Activities:
Net Income	$ 28,925	$ 27,808	$ 26,582
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	8,823	8,723	8,592
Deferred income taxes	(1,431)	2	(923)
Stock-based compensation	1,841	2,209	1,586
Impairment of investment	2,413	0	0
Net change in accrued interest, premiums, and discounts on investments	100	340	556
Other	17	29	30
Net Cash Provided By Used In Operating Activities Before Changes In Operating Capital, Total	40,688	39,111	36,423
Changes in operating assets and liabilities:
Accounts receivable	371	(2,798)	(1,110)
Inventories	(1,749)	(1,756)	(2,487)
Prepaid expenses and other current assets	1,786	(3,117)	1,507
Other non-current assets	(103)	(22)	(17)
Accounts payable and accrued liabilities	(492)	968	1,768
Accrued income and other taxes	(128)	(396)	388
Other non-current liabilities	54	(767)	104
Net Cash Provided by (Used in) Operating Activities, Total	40,427	31,223	36,576
Cash Flows From Investing Activities:
Property, plant and equipment additions	(9,323)	(12,671)	(7,503)
Purchase of patents	0	0	(2,150)
Purchase of investments	(168)	(33,115)	0
Proceeds from maturities of investments	13,400	35,975	7,639
Net Cash Provided by (Used in) Investing Activities, Total	3,909	(9,811)	(2,014)
Cash Flows From Financing Activities:
Shares tendered for employees' withholding taxes on stock-based compensation	(154)	(376)	0
Tax benefit related to stock-based compensation	156	168	15
Purchase of treasury stock	(30,698)	(23,556)	(9,196)
Dividends paid	(6,069)	(5,432)	(4,821)
Net Cash Provided by (Used in) Financing Activities, Total	(36,765)	(29,196)	(14,002)
Net change in cash and cash equivalents	7,571	(7,784)	20,560
Cash and cash equivalents, beginning of year	20,775	28,559	7,999
Cash and cash equivalents, end of year	28,346	20,775	28,559
Cash paid for:
Income taxes	$ 12,900	$ 17,475	$ 8,036