Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Cash flows from operating activities:
Net income	$ 21,768	$ 20,813
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	6,696	6,388
Deferred income taxes	(1,463)	(608)
Stock-based compensation	1,836	1,215
Net change in accrued interest, premiums, and discounts on investments	242	424
Other	30	26
Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities	29,109	28,258
Changes in operating assets and liabilities:
Accounts receivable	(4,235)	(3,129)
Inventories	(2,142)	(2,709)
Prepaid expenses	(371)	1,518
Other non-current assets	(70)	(17)
Accounts payable and accrued liabilities	1,380	2,525
Accrued income and other taxes	37	1,172
Other non-current liabilities	(448)	(198)
Net Cash Provided by (Used in) Operating Activities, Continuing Operations, Total	23,260	27,420
Cash flows from investing activities:
Property, plant and equipment additions	(8,641)	(4,713)
Purchase of investments	(19,375)
Proceeds from maturities of investments	19,375	7,639
Net Cash Provided by (Used in) Investing Activities, Continuing Operations, Total	(8,641)	2,926
Cash flows from financing activities:
Shares tendered for employees' withholding taxes on stock-based compensation	(377)	0
Tax benefit related to stock-based compensation	160	6
Purchase of treasury stock	(12,065)	(4,086)
Dividends paid	(3,975)	(3,541)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations, Total	(16,257)	(7,621)
Net change in cash and cash equivalents	(1,638)	22,725
Cash and cash equivalents at beginning of period	28,559	7,999
Cash and cash equivalents at end of period	26,921	30,724
Cash paid for:
Income taxes	$ 13,393	$ 7,927