Summary of Significant Accounting Policies Investments in Marketable Securities (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended		12 Months Ended
	Sep. 30, 2013		Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 167,788		$ 90,648
Available-for-sale Securities, Gross Unrealized Gains	60		20
Available-for-sale Securities, Gross Unrealized Losses	(850)		(1,193)
Available-for-sale Securities, Fair Value Disclosure	166,998		89,475
US Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis	167,788	[1]	87,394
Available-for-sale Securities, Gross Unrealized Gains	60	[1]	20
Available-for-sale Securities, Gross Unrealized Losses	(850)	[1]	(411)
Available-for-sale Securities, Fair Value Disclosure	166,998	[1]	87,003
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Amortized Cost Basis			3,254
Available-for-sale Securities, Gross Unrealized Gains			0
Available-for-sale Securities, Gross Unrealized Losses			(782)
Available-for-sale Securities, Fair Value Disclosure			$ 2,472

[1] (1) Maturity dates ranging from 2013 to 2014.