Segment Information - Schedule of Segment Information (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Segment Reporting [Abstract]
Internally allocated interest costs, pre tax rate	6.00%	6.00%	6.25%
Capital structure assumption, debt to equity ratio	50.00%
Mineral rights	$ 12.1	$ 13.4	$ 15.0

Carrying amount at the balance sheet date of mineral rights, or rights to extract a mineral from the earth or to receive payment in the form of a royalty for the extraction of minerals, net of amortization.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Mineral Rights

-URI http://asc.fasb.org/extlink&oid=6919630

Name:	us-gaap_MineralRights
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant