Fair Value Measurements (Fair Values of the Company’s Financial Assets and Liabilities) (Details) - Recurring Basis - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Restricted short-term investments:
Fair value measurement	$ 36,841	$ 43,771
Money market accounts
Cash equivalents:
Cash equivalents	35,556	42,486
Certificates of deposit
Restricted short-term investments:
Restricted short-term investments	1,285	1,285
Level 1
Restricted short-term investments:
Fair value measurement	36,841	43,771
Level 1 | Money market accounts
Cash equivalents:
Cash equivalents	35,556	42,486
Level 1 | Certificates of deposit
Restricted short-term investments:
Restricted short-term investments	$ 1,285	$ 1,285