Basis of Presentation and Accounting Policies (Details 2) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Cash, Cash Equivalents and Marketable Securities
Cash and cash equivalents	$ 146,470,000	$ 18,130,000	$ 12,416,000	$ 13,245,000
Available-for-sale securities	49,897,000	50,027,000
Net realized gains or losses	0	0
Research and Development
Prepaid research and development costs	$ 3,600,000	$ 3,600,000
Furniture and equipment | Minimum
Cash, Cash Equivalents and Marketable Securities
Estimated useful lives	2 years
Furniture and equipment | Maximum
Cash, Cash Equivalents and Marketable Securities
Estimated useful lives	5 years