Fair Value Measurements - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Millions	Jun. 30, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Valuation Adjustment For Level Three Asset and Liability	$ 6.8
Auction rate securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Valuation Adjustment For Level Three Asset and Liability	6.1
Auction Rate Securities Purchase Commitment
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Valuation Adjustment For Level Three Asset and Liability	$ 0.7