Summary of Significant Accounting Policies Investments in Marketable Securities (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 37,270	$ 58,819
Available-for-sale Securities, Gross Unrealized Gains	10	2
Available-for-sale Securities, Gross Unrealized Losses	(190)	(263)
Available-for-sale Securities, Fair Value Disclosure	37,090	58,558
US Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	37,270	58,819
Available-for-sale Securities, Gross Unrealized Gains	10	2
Available-for-sale Securities, Gross Unrealized Losses	(190)	(263)
Available-for-sale Securities, Fair Value Disclosure	$ 37,090	$ 58,558