Short-Term debt (Details)	Mar. 31, 2011
Short-term debt (Textuals)
Average annual interest rate on short-term borrowings from commercial banks for import financing	1.99%

Reflects the calculation as of the balance-sheet date of the average interest rate weighted by the amount of short-term debt outstanding by type or by instrument at that time.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19
-Subparagraph b
-Article 5

Name:	us-gaap_ShortTermDebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap
Data Type:	us-types:percentItemType
Balance Type:	na
Period Type:	instant