Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net income	$ 9,950	$ 6,945
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,099	2,212
Deferred income taxes	217	(168)
Stock-based compensation	275	491
Bond impairment	0	345
Net change in accrued interest, premiums, and discounts on investments	(28)	5
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities	12,513	9,830
Changes in operating assets and liabilities:
Accounts receivable	(3,513)	(5,097)
Inventories	(1,339)	(697)
Prepaid expenses	1,178	1,562
Other non-current assets	66	(62)
Accounts payable and accrued liabilities	773	(487)
Accrued income and other taxes	278	2,209
Other non-current liabilities	39	(120)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations, Total	9,995	7,138
Cash flows from investing activities:
Property, plant and equipment additions	(2,373)	(2,947)
Purchase of investments	(19,911)	(1,676)
Proceeds from maturities of investments	15,000	0
Net Cash Provided by (Used in) Investing Activities, Continuing Operations, Total	(7,284)	(4,623)
Cash flows from financing activities:
Shares tendered for employees’ withholding taxes on stock-based compensation	(3,275)	0
Purchase of treasury stock	0	(1,276)
Dividends paid	(1,929)	(1,638)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations, Total	(5,204)	(2,914)
Net change in cash and cash equivalents	(2,493)	(399)
Cash and cash equivalents at beginning of period	20,022	28,346
Cash and cash equivalents at end of period	17,529	27,947
Cash paid for:
Income taxes	29	104
Non-cash financing activities:
Non-cash effect of stock option exercises	$ 4,535	$ 0