Segment and Geographical Information - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($) segment core_business_area
Segment Reporting [Abstract]
Number of reportable segments \| segment	5
Sales of timberland (exceed) \| $	$ 20
Trading
Segment Reporting Information [Line Items]
Number of core business areas \| core_business_area	2

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

No definition available.

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration