Summary of Significant Accounting Policies Investments in Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended		12 Months Ended
	Jun. 30, 2014		Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 75,589		$ 130,971
Available-for-sale Securities, Gross Unrealized Gains	6		21
Available-for-sale Securities, Gross Unrealized Losses	(797)		(975)
Available-for-sale Securities, Fair Value Disclosure	74,798		130,017
US Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	75,589	[1]	130,971
Available-for-sale Securities, Gross Unrealized Gains	6	[1]	21
Available-for-sale Securities, Gross Unrealized Losses	(797)	[1]	(975)
Available-for-sale Securities, Fair Value Disclosure	$ 74,798	[1]	$ 130,017

[1] (1) Maturity dates ranging from 2014 to 2015.