Conversion Features (Details) $ in Millions |
9 Months Ended | 12 Months Ended |
|---|---|---|
Dec. 31, 2017 |
Mar. 31, 2018
USD ($)
day
|
|
| 2015 Senior Subordinated Convertible Debt | ||
| Debt Instrument [Line Items] | ||
| Threshold percentage of stock price trigger | 130.00% | |
| If-converted value in excess of principal | $ | $ 1,141.7 | |
| Convertible Debt | ||
| Debt Instrument [Line Items] | ||
| Debt Instrument, Redemption Price, Percentage | 100.00% | |
| Convertible Debt | Debt Instrument, Redemption, Period One | ||
| Debt Instrument [Line Items] | ||
| Threshold percentage of stock price trigger | 130.00% | |
| Threshold trading days | 20 | |
| Threshold consecutive trading days | 30 | |
| Convertible Debt | Debt Instrument, Redemption, Period Two | ||
| Debt Instrument [Line Items] | ||
| Threshold percentage of stock price trigger | 98.00% | |
| Threshold trading days | 5 | |
| Threshold consecutive trading days | 10 |