Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Major categories of assets and liabilities measured on a recurring basis, at fair value
Assets held for sale	$ 6,000
Assets and liabilities measured on a recurring basis | Level 1 | U.S. treasuries
Major categories of assets and liabilities measured on a recurring basis, at fair value
Cash equivalents and short-term investments	81,527	130,977
Assets and liabilities measured on a recurring basis | Level 2
Major categories of assets and liabilities measured on a recurring basis, at fair value
Assets held for sale	6,000
Derivative instrument		907
Assets and liabilities measured on a recurring basis | Level 2 | Corporate debt
Major categories of assets and liabilities measured on a recurring basis, at fair value
Cash equivalents and short-term investments	39,045	77,601
Assets and liabilities measured on a recurring basis | Level 2 | Government agency securities
Major categories of assets and liabilities measured on a recurring basis, at fair value
Cash equivalents and short-term investments		61,013
Assets and liabilities measured on a recurring basis | Level 2 | Commercial paper
Major categories of assets and liabilities measured on a recurring basis, at fair value
Cash equivalents and short-term investments		11,947
Assets and liabilities measured on a recurring basis | Level 3
Major categories of assets and liabilities measured on a recurring basis, at fair value
Contingent consideration		(29,368)
Assets and liabilities measured on a recurring basis | Total
Major categories of assets and liabilities measured on a recurring basis, at fair value
Assets held for sale	6,000
Derivative instrument		907
Contingent consideration		(29,368)
Assets and liabilities measured on a recurring basis | Total | U.S. treasuries
Major categories of assets and liabilities measured on a recurring basis, at fair value
Cash equivalents and short-term investments	81,527	130,977
Assets and liabilities measured on a recurring basis | Total | Corporate debt
Major categories of assets and liabilities measured on a recurring basis, at fair value
Cash equivalents and short-term investments	39,045	77,601
Assets and liabilities measured on a recurring basis | Total | Government agency securities
Major categories of assets and liabilities measured on a recurring basis, at fair value
Cash equivalents and short-term investments		61,013
Assets and liabilities measured on a recurring basis | Total | Commercial paper
Major categories of assets and liabilities measured on a recurring basis, at fair value
Cash equivalents and short-term investments		$ 11,947