Fair Value Measurements (Hierarchy) (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Financial Assets:
Total financial assets	$ 204,860	$ 207,552
Current Liabilities:
Warrants	3,139	3,649
Total financial liabilities	3,139	3,649
Money market deposits
Financial Assets:
Total financial assets	8,263	5,966
U.S. Treasury securities
Financial Assets:
Total financial assets	103,096	103,813
U.S. agency securities
Financial Assets:
Total financial assets	74,616	78,853
Municipal securities
Financial Assets:
Total financial assets	18,885	18,920
Level 1
Financial Assets:
Total financial assets	111,359	109,779
Level 1 | Money market deposits
Financial Assets:
Total financial assets	8,263	5,966
Level 1 | U.S. Treasury securities
Financial Assets:
Total financial assets	103,096	103,813
Level 2
Financial Assets:
Total financial assets	93,501	97,773
Level 2 | U.S. agency securities
Financial Assets:
Total financial assets	74,616	78,853
Level 2 | Municipal securities
Financial Assets:
Total financial assets	18,885	18,920
Level 3
Current Liabilities:
Warrants	3,139	3,649
Total financial liabilities	$ 3,139	$ 3,649