Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Statement of Cash Flows [Abstract]
Net cash flows provided by operating activities	$ 5,352	$ 1,597
Cash flows from investing activities:
Purchases of property, plant and equipment	(5,290)	(6,131)
Purchases of long-term marketable securities	(154)	(408)
Proceeds from sale of long-term marketable securities	62	348
Other	0	12
Net cash flows used in investing activities	(5,382)	(6,179)
Cash flows from financing activities:
Dividends paid	(3,753)	(3,737)
Proceeds from the issuance of common stock	0	361
Excess tax benefits from the exercise of stock options	0	25
Net cash flows used in financing activities	(3,753)	(3,351)
Effect of exchange rate changes on cash and cash equivalents	(217)	154
Net decrease in cash and cash equivalents	(4,000)	(7,779)
Cash and cash equivalents at beginning of period	97,098	97,910
Cash and cash equivalents at end of period	93,098	90,131
Supplemental information:
Income tax payments	3,082	3,161
Interest payments	110	109
Non-cash investing activities:
Purchases of property, plant and equipment included in accounts payable	$ 424	$ 542