Fair Value Measurements (Fair Value Hierarchy) (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets
Corporate debt and auction rate securities	$ 23,917	$ 32,945
Level 1 [Member]
Assets
Corporate debt and auction rate securities
Total investments
Liabilities:
Warrant liabilities
Level 2 [Member]
Assets
Corporate debt and auction rate securities	23,917	32,945
Total investments	23,917	32,945
Liabilities:
Warrant liabilities
Level 3 [Member]
Assets
Corporate debt and auction rate securities
Total investments
Liabilities:
Warrant liabilities		$ 267