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Fair Value Measurements - Narrative (Details)
Mar. 31, 2019
1.125% Call Option  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Percentage of contractual interest rate on derivative 1.125%
1.125% Conversion Option  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Percentage of contractual interest rate on derivative 1.125%