Investments (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Jan. 31, 2015	Dec. 31, 2014	Apr. 30, 2013	Mar. 31, 2013
Schedule of Equity Method Investments [Line Items]
Carrying value	$ 138,218		$ 117,733
J-Devices [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value	$ 138,218		$ 117,733
Ownership interest	65.70%	65.70%	60.00%	60.00%	30.00%