Segment Information (Details) (USD $)	3 Months Ended
	Mar. 31, 2013 item	Mar. 31, 2012	Dec. 31, 2012
Segment Information
Number of operating segments	1
Segment information
Revenues derived from foreign subsidiaries	$ 25,143,000	$ 26,847,000
Identifiable assets	60,511,000		60,967,000
Wholly owned foreign subsidiaries
Segment information
Revenues derived from foreign subsidiaries	11,093,000	10,832,000
Identifiable assets	27,174,000	24,524,000
All subsidiaries
Segment information
Sales to customers outside of the United States	$ 12,305,000	$ 12,330,000