Quarterly report pursuant to Section 13 or 15(d)

Fair Value - Schedule of fair value of financial assets and liabilities (Details)

v3.2.0.727
Fair Value - Schedule of fair value of financial assets and liabilities (Details) - USD ($)
$ in Thousands
Jun. 30, 2015
Dec. 31, 2014
Assets:    
Total assets measured at fair value $ 362,454 $ 386,344
Money market funds    
Assets:    
Total assets measured at fair value 94,948 89,113
Commercial paper    
Assets:    
Total assets measured at fair value 50,331 54,792
Corporate debt securities    
Assets:    
Total assets measured at fair value 214,673 234,697
U.S. government and government agency debt securities    
Assets:    
Total assets measured at fair value 2,502 7,742
Quoted Prices in Active Markets for Identical Instruments (Level 1)    
Assets:    
Total assets measured at fair value 94,948 89,113
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Money market funds    
Assets:    
Total assets measured at fair value 94,948 89,113
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Commercial paper    
Assets:    
Total assets measured at fair value 0 0
Quoted Prices in Active Markets for Identical Instruments (Level 1) | Corporate debt securities    
Assets:    
Total assets measured at fair value 0 0
Quoted Prices in Active Markets for Identical Instruments (Level 1) | U.S. government and government agency debt securities    
Assets:    
Total assets measured at fair value 0 0
Significant Other Observable Inputs (Level 2)    
Assets:    
Total assets measured at fair value 267,506 297,231
Significant Other Observable Inputs (Level 2) | Money market funds    
Assets:    
Total assets measured at fair value 0 0
Significant Other Observable Inputs (Level 2) | Commercial paper    
Assets:    
Total assets measured at fair value 50,331 54,792
Significant Other Observable Inputs (Level 2) | Corporate debt securities    
Assets:    
Total assets measured at fair value 214,673 234,697
Significant Other Observable Inputs (Level 2) | U.S. government and government agency debt securities    
Assets:    
Total assets measured at fair value $ 2,502 $ 7,742