Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities:
Net income	$ 19,976	$ 14,396
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	4,223	4,442
Deferred income taxes	1,009	225
Stock-based compensation	903	1,081
Bond impairment	0	345
Net change in accrued interest, premiums, and discounts on investments	(82)	38
Other	(2)	0
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities	26,027	20,527
Changes in operating assets and liabilities:
Accounts receivable	(2,524)	(2,213)
Inventories	(950)	(1,396)
Prepaid expenses	(2,841)	(881)
Other non-current assets	81	(130)
Accounts payable and accrued liabilities	(552)	(1,411)
Accrued income and other taxes	862	331
Other non-current liabilities	39	193
Net Cash Provided by (Used in) Operating Activities, Continuing Operations, Total	20,142	15,020
Cash flows from investing activities:
Property, plant and equipment additions	(5,422)	(5,292)
Purchase of investments	(21,911)	(6,799)
Proceeds from sale of investments	0	210
Proceeds from maturities of investments	19,000	5,000
Net Cash Provided by (Used in) Investing Activities, Continuing Operations, Total	(8,333)	(6,881)
Cash flows from financing activities:
Shares tendered for employees’ withholding taxes on stock-based compensation	(7,735)	(1,112)
Purchase of treasury stock	0	(1,276)
Dividends paid	(3,873)	(3,280)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations, Total	(11,608)	(5,668)
Net change in cash and cash equivalents	201	2,471
Cash and cash equivalents at beginning of period	20,022	28,346
Cash and cash equivalents at end of period	20,223	30,817
Cash paid for:
Income taxes	2,295	5,860
Non-cash financing activities:
Non-cash effect of stock option exercises	$ 10,237	$ 0