Debt (Tables)	12 Months Ended
Dec. 31, 2017
Debt Instrument [Line Items]
Schedule of Long-term Debt Instruments
Interest Expense Associated with Convertible Notes	Total interest expense associated with the Notes, net of capitalized interest as applicable, was not material in 2016 and 2015.

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

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+ Details