Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities:
Net income	$ 9,438	$ 8,487
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,546	2,183
Deferred income taxes	627	(138)
Stock-based compensation	380	316
Net change in unrealized gains and losses on investments	(147)	789
Net change in accrued interest, premiums, and discounts on investments	184	(104)
Total adjustments	13,028	11,533
Changes in operating assets and liabilities:
Accounts receivable	(4,226)	(3,528)
Inventories	771	(553)
Prepaid expenses	1,439	1,135
Other non-current assets	34	(252)
Accounts payable and accrued liabilities	316	(668)
Accrued income and other taxes	477	2,229
Other non-current liabilities	1,066	470
Net Cash Provided by (Used in) Operating Activities, Continuing Operations, Total	12,905	10,366
Cash flows from investing activities:
Property, plant and equipment additions	(3,563)	(3,269)
Purchase of investments	(28,218)	(25,521)
Proceeds from maturities of investments	6,667	10,691
Net Cash Provided by (Used in) Investing Activities, Continuing Operations, Total	(25,114)	(18,099)
Cash flows from financing activities:
Dividends paid	(2,501)	(2,222)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations, Total	(2,501)	(2,222)
Net change in cash and cash equivalents	(14,710)	(9,955)
Cash and cash equivalents at beginning of period	58,753	30,136
Cash and cash equivalents at end of period	44,043	20,181
Cash paid for:
Income taxes	$ 56	$ 24