Derivative Financial Instruments and Fair Value Measurements - Narrative (Detail)	12 Months Ended
Dec. 31, 2017
Minimum
Derivative [Line Items]
Anticipated requirements, Outstanding purchase commitment	1 month
Maximum
Derivative [Line Items]
Anticipated requirements, Outstanding purchase commitment	1 year

Period covered by the long-term purchase commitment, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

No definition available.

Name:	us-gaap_LongtermPurchaseCommitmentPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration