Description of Business and Summary of Significant Accounting Policies (Revenues by product line and geographic area) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Revenue from External Customer [Line Items]
Total	$ 52,918	$ 41,593	$ 46,074	$ 46,001	$ 38,979	$ 51,197	$ 55,610	$ 47,748	$ 186,586		$ 193,534		$ 159,258
China [Member]
Revenue from External Customer [Line Items]
Total									89,143		92,817		74,054
United States [Member]
Revenue from External Customer [Line Items]
Total									23,758		29,090		26,473
Germany [Member]
Revenue from External Customer [Line Items]
Total									16,384		25,935		25,119
All other countries [Member]
Revenue from External Customer [Line Items]
Total									57,301	[1]	45,692	[1]	33,612	[1]
Ultracapacitors [Member]
Revenue from External Customer [Line Items]
Total									135,637		136,277		95,953
High-Voltage Capacitors [Member]
Revenue from External Customer [Line Items]
Total									40,361		43,339		45,574
Microelectronic Products [Member]
Revenue from External Customer [Line Items]
Total									$ 10,588		$ 13,918		$ 17,731

[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.