Principles of Consolidation - Fair Value Measurements (Details) - Fair Value, Measurements, Recurring $ in Millions	Mar. 31, 2019 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	$ 25.0
Total assets at fair value	25.0
Quoted prices in active market (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	25.0
Total assets at fair value	25.0
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	0.0
Total assets at fair value	0.0
Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Restricted amounts held in escrow-current	0.0
Total assets at fair value	$ 0.0