Fair Value Measurements (Details) - USD ($) $ in Millions | Jun. 30, 2020 | Dec. 31, 2019 |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | $ 334.1 | $ 551.3 |
Total short-term investments | 783.5 | 607.7 |
Supranational securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | | 4 |
Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 361.4 | 286.6 |
US Treasury securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 235.8 | 171.3 |
Asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 83.6 | 53.8 |
Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 40 | 24.2 |
US Agency securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 27.9 | 27.2 |
Certificates of deposit | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 26 | 38.2 |
Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 6 | 2.4 |
Foreign government obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 2.8 | |
Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 1.1 | |
Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 241.5 | 444.3 |
Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 1.8 | |
Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 1.2 | 2 |
Level 3 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Equity investments | 5.6 | |
Fair Value, Measurements, Recurring | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 783.5 | 607.7 |
Total cash equivalents and short-term investments | 1,029.1 | |
Equity investments | | 9.8 |
Total | | 1,063.8 |
Fair Value, Measurements, Recurring | Supranational securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | | 4 |
Fair Value, Measurements, Recurring | Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 361.4 | 286.6 |
Fair Value, Measurements, Recurring | US Treasury securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 235.8 | 171.3 |
Fair Value, Measurements, Recurring | Asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 83.6 | 53.8 |
Fair Value, Measurements, Recurring | Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 40 | 24.2 |
Fair Value, Measurements, Recurring | US Agency securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 27.9 | 27.2 |
Fair Value, Measurements, Recurring | Certificates of deposit | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 26 | 38.2 |
Fair Value, Measurements, Recurring | Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 6 | 2.4 |
Fair Value, Measurements, Recurring | Foreign government obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 2.8 | |
Fair Value, Measurements, Recurring | Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 1.1 | |
Fair Value, Measurements, Recurring | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 241.5 | 444.3 |
Fair Value, Measurements, Recurring | Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 1.8 | |
Fair Value, Measurements, Recurring | Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 1.2 | 2 |
Fair Value, Measurements, Recurring | Cash equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 245.6 | 446.3 |
Fair Value, Measurements, Recurring | Level 1 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Total cash equivalents and short-term investments | 241.5 | |
Equity investments | | 9.8 |
Total | | 454.1 |
Fair Value, Measurements, Recurring | Level 1 | Supranational securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | | 0 |
Fair Value, Measurements, Recurring | Level 1 | Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | US Treasury securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | US Agency securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Certificates of deposit | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Foreign government obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | |
Fair Value, Measurements, Recurring | Level 1 | Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 0 | |
Fair Value, Measurements, Recurring | Level 1 | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 241.5 | 444.3 |
Fair Value, Measurements, Recurring | Level 1 | Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 0 | |
Fair Value, Measurements, Recurring | Level 1 | Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 0 | 0 |
Fair Value, Measurements, Recurring | Level 1 | Cash equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 241.5 | 444.3 |
Fair Value, Measurements, Recurring | Level 2 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 783.5 | 607.7 |
Total cash equivalents and short-term investments | 787.6 | |
Equity investments | | 0 |
Total | | 609.7 |
Fair Value, Measurements, Recurring | Level 2 | Supranational securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | | 4 |
Fair Value, Measurements, Recurring | Level 2 | Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 361.4 | 286.6 |
Fair Value, Measurements, Recurring | Level 2 | US Treasury securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 235.8 | 171.3 |
Fair Value, Measurements, Recurring | Level 2 | Asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 83.6 | 53.8 |
Fair Value, Measurements, Recurring | Level 2 | Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 40 | 24.2 |
Fair Value, Measurements, Recurring | Level 2 | US Agency securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 27.9 | 27.2 |
Fair Value, Measurements, Recurring | Level 2 | Certificates of deposit | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 26 | 38.2 |
Fair Value, Measurements, Recurring | Level 2 | Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 6 | 2.4 |
Fair Value, Measurements, Recurring | Level 2 | Foreign government obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 2.8 | |
Fair Value, Measurements, Recurring | Level 2 | Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 1.1 | |
Fair Value, Measurements, Recurring | Level 2 | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 0 | 0 |
Fair Value, Measurements, Recurring | Level 2 | Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 1.8 | |
Fair Value, Measurements, Recurring | Level 2 | Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 1.2 | 2 |
Fair Value, Measurements, Recurring | Level 2 | Cash equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 4.1 | 2 |
Fair Value, Measurements, Recurring | Level 3 | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Total cash equivalents and short-term investments | 0 | |
Equity investments | | 0 |
Total | | 0 |
Fair Value, Measurements, Recurring | Level 3 | Supranational securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | | 0 |
Fair Value, Measurements, Recurring | Level 3 | Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | US Treasury securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Asset-backed securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | US Agency securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Certificates of deposit | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Foreign government obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total short-term investments | 0 | |
Fair Value, Measurements, Recurring | Level 3 | Corporate notes and obligations | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 0 | |
Fair Value, Measurements, Recurring | Level 3 | Money market funds | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Municipal securities | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 0 | |
Fair Value, Measurements, Recurring | Level 3 | Commercial paper | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | 0 | 0 |
Fair Value, Measurements, Recurring | Level 3 | Cash equivalents | | |
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | | |
Total cash equivalents | $ 0 | $ 0 |