The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 159

-Paragraph 18

-Subparagraph f

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 18

-Paragraph 20

-Subparagraph a (1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Investments in Non-Consolidated Affiliates (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended
	Mar. 31, 2012	Jun. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
Investments in Non-Consolidated Affiliates
Initial payment received from the sale of the joint venture	$ 37.6
Installment payments received from the sale of the joint venture		4.7	9.4	14.1
Remaining principal amount due from sale of joint venture		$ 48	$ 48
PIGAP II
Ownership interest of each equity method investee
Ownership Interest (as a percent)		30.00%	30.00%
El Furrial
Ownership interest of each equity method investee
Ownership Interest (as a percent)		33.30%	33.30%