Derivative Instruments (Details 7) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013 MMBTU	Dec. 31, 2012 MMBTU
Natural gas contracts
Derivative Instruments
Outstanding derivative contracts that were entered into to hedge forecasted transactions (in mmbtu)	70,000	235,000
Foreign exchange contracts
Derivative Instruments
Outstanding derivative contracts that were entered into to hedge forecasted transactions	41,920	42,399

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

Name:	invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant