Condensed Consolidated Statements of Cash Flows (Unaudited) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Statement of Cash Flows [Abstract]
Net cash flows provided by operating activities	$ 9,694	$ 28,957
Cash flows from investing activities:
Purchases of property, plant and equipment	(10,217)	(10,264)
Purchases of long-term marketable securities	(667)	(810)
Proceeds from sale of long-term marketable securities	603	678
Other	185	6
Net cash flows used in investing activities	(10,096)	(10,390)
Cash flows from financing activities:
Dividends paid	(5,613)	(5,590)
Proceeds from the issuance of common stock	581	67
Excess tax benefits from the exercise of stock options	60	2
Net cash flows used in financing activities	(4,972)	(5,521)
Effect of exchange rate changes on cash and cash equivalents	(563)	340
Net (decrease) increase in cash and cash equivalents	(5,937)	13,386
Cash and cash equivalents at beginning of period	97,910	78,889
Cash and cash equivalents at end of period	91,973	92,275
Supplemental information:
Income tax payments	3,406	877
Interest payments	169	182
Non-cash investing activities:
Purchases of property, plant and equipment included in accounts payable	$ 694	$ 677