Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands | Jun. 30, 2015 | Dec. 31, 2014 |
Fair value [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | $ 556,145 | $ 26,019 |
Total short-term investments | 463,137 | 255,845 |
Total assets measured at fair value | 1,019,282 | 281,864 |
Certificates of deposit [Member] | Fair value [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 11,482 | 4,994 |
Commercial paper [Member] | Fair value [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 4,998 | 0 |
Corporate notes and bonds [Member] | Fair value [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 286,828 | 142,984 |
U.S. Government agencies [Member] | Fair value [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 159,829 | 107,867 |
Money market funds [Member] | Fair value [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 300,064 | 13,069 |
Commercial paper [Member] | Fair value [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 59,991 | 0 |
U.S. Government agencies [Member] | Fair value [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 196,090 | 12,950 |
Level 1 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 300,064 | 13,069 |
Total short-term investments | 0 | 0 |
Total assets measured at fair value | 300,064 | 13,069 |
Level 1 [Member] | Certificates of deposit [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 0 | 0 |
Level 1 [Member] | Commercial paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 0 | 0 |
Level 1 [Member] | Corporate notes and bonds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 0 | 0 |
Level 1 [Member] | U.S. Government agencies [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 0 | 0 |
Level 1 [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 300,064 | 13,069 |
Level 1 [Member] | Commercial paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 0 | 0 |
Level 1 [Member] | U.S. Government agencies [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 0 | 0 |
Level 2 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 256,081 | 12,950 |
Total short-term investments | 463,137 | 255,845 |
Total assets measured at fair value | 719,218 | 268,795 |
Level 2 [Member] | Certificates of deposit [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 11,482 | 4,994 |
Level 2 [Member] | Commercial paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 4,998 | 0 |
Level 2 [Member] | Corporate notes and bonds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 286,828 | 142,984 |
Level 2 [Member] | U.S. Government agencies [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 159,829 | 107,867 |
Level 2 [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 0 | 0 |
Level 2 [Member] | Commercial paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 59,991 | 0 |
Level 2 [Member] | U.S. Government agencies [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 196,090 | 12,950 |
Level 3 [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 0 | 0 |
Total short-term investments | 0 | 0 |
Total assets measured at fair value | 0 | 0 |
Level 3 [Member] | Certificates of deposit [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 0 | 0 |
Level 3 [Member] | Commercial paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 0 | 0 |
Level 3 [Member] | Corporate notes and bonds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 0 | 0 |
Level 3 [Member] | U.S. Government agencies [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total short-term investments | 0 | 0 |
Level 3 [Member] | Money market funds [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 0 | 0 |
Level 3 [Member] | Commercial paper [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | 0 | 0 |
Level 3 [Member] | U.S. Government agencies [Member] | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Total cash equivalents | $ 0 | $ 0 |