Description of Business and Summary of Significant Accounting Policies (Revenues by product line and geographic area) (Details) - USD ($) $ in Thousands		3 Months Ended								12 Months Ended
		Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue from External Customer [Line Items]
Total		$ 49,830	$ 45,076	$ 37,796	$ 34,670	$ 52,918	$ 41,593	$ 46,074	$ 46,001	$ 167,372	$ 186,586	$ 193,534
China [Member]
Revenue from External Customer [Line Items]
Total										87,856	89,143	92,817
United States [Member]
Revenue from External Customer [Line Items]
Total										20,836	23,758	29,090
Germany
Revenue from External Customer [Line Items]
Total										13,972	16,384	25,935
All other countries [Member]
Revenue from External Customer [Line Items]
Total	[1]									44,708	57,301	45,692
Ultracapacitors [Member]
Revenue from External Customer [Line Items]
Total										114,525	135,637	136,277
High-Voltage Capacitors [Member]
Revenue from External Customer [Line Items]
Total										41,718	40,361	43,339
Microelectronic Products [Member]
Revenue from External Customer [Line Items]
Total										$ 11,129	$ 10,588	$ 13,918

[1] Revenue from external customers located in countries included in “All other countries” do not individually comprise more than 10% of total revenues for any of the years presented.