Fair Value Measurements (Details) (Fair Value, Measurements, Recurring, USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair value of assets and liabilities measured on a recurring basis
Transfers or reclassifications of securities from Level 1 to Level 2	$ 0
Transfers or reclassifications of securities from Level 2 to Level 1	0
Estimate of Fair Value Measurement
Fair value of assets and liabilities measured on a recurring basis
Total Assets	311,206	102,144
Total Liabilities	221,259	218,702
Estimate of Fair Value Measurement | PlasmaTech Biopharmaceuticals Inc
Fair value of assets and liabilities measured on a recurring basis
Total Liabilities	12,222	12,102
Estimate of Fair Value Measurement | Acquisition Related Contingent Consideration | Lumara Health
Fair value of assets and liabilities measured on a recurring basis
Total Liabilities	209,037	206,600
Estimate of Fair Value Measurement | Money market funds
Fair value of assets and liabilities measured on a recurring basis
Total Assets	193,868	77,254
Estimate of Fair Value Measurement | Corporate debt securities
Fair value of assets and liabilities measured on a recurring basis
Total Assets	62,567	24,890
Estimate of Fair Value Measurement | Commercial paper
Fair value of assets and liabilities measured on a recurring basis
Total Assets	30,461
Estimate of Fair Value Measurement | Certificates of deposit
Fair value of assets and liabilities measured on a recurring basis
Total Assets	14,999
Estimate of Fair Value Measurement | Municipal securities
Fair value of assets and liabilities measured on a recurring basis
Total Assets	9,311
Fair Value, Inputs, Level 1
Fair value of assets and liabilities measured on a recurring basis
Total Assets	193,868	77,254
Fair Value, Inputs, Level 1 | Money market funds
Fair value of assets and liabilities measured on a recurring basis
Total Assets	193,868	77,254
Fair Value, Inputs, Level 2
Fair value of assets and liabilities measured on a recurring basis
Total Assets	117,338	24,890
Fair Value, Inputs, Level 2 | Corporate debt securities
Fair value of assets and liabilities measured on a recurring basis
Total Assets	62,567	24,890
Fair Value, Inputs, Level 2 | Commercial paper
Fair value of assets and liabilities measured on a recurring basis
Total Assets	30,461
Fair Value, Inputs, Level 2 | Certificates of deposit
Fair value of assets and liabilities measured on a recurring basis
Total Assets	14,999
Fair Value, Inputs, Level 2 | Municipal securities
Fair value of assets and liabilities measured on a recurring basis
Total Assets	9,311
Fair Value, Inputs, Level 3
Fair value of assets and liabilities measured on a recurring basis
Total Liabilities	221,259	218,702
Fair Value, Inputs, Level 3 | PlasmaTech Biopharmaceuticals Inc
Fair value of assets and liabilities measured on a recurring basis
Total Liabilities	12,222	12,102
Fair Value, Inputs, Level 3 | Acquisition Related Contingent Consideration | Lumara Health
Fair value of assets and liabilities measured on a recurring basis
Total Liabilities	$ 209,037	$ 206,600