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, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Revenue from External Customer [Line Items]
Total	$ 38,979	$ 51,197	$ 55,610	$ 47,748	$ 44,503	$ 42,713	$ 36,238	$ 35,804	$ 193,534		$ 159,258		$ 147,176
China [Member]
Revenue from External Customer [Line Items]
Total									92,817		74,054		43,187
Germany [Member]
Revenue from External Customer [Line Items]
Total									25,935		25,119		26,253
United States [Member]
Revenue from External Customer [Line Items]
Total									29,090		26,473		29,723
All other countries [Member]
Revenue from External Customer [Line Items]
Total									45,692	[1]	33,612	[1]	48,013	[1]
Ultracapacitors [Member]
Revenue from External Customer [Line Items]
Total									136,277		95,953		86,836
High-Voltage Capacitors [Member]
Revenue from External Customer [Line Items]
Total									43,339		45,574		42,309
Microelectronic Products [Member]
Revenue from External Customer [Line Items]
Total									$ 13,918		$ 17,731		$ 18,031

[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.