Derivative Instruments and Hedging Activities - Commitment of Cross Currency Swaps (Parenthetical) (Detail) (NOK) In Millions, unless otherwise specified	Jun. 30, 2013	Jan. 31, 2013
Derivative [Line Items]
Repurchase of bond		388.5
Bond issue, original value	600
Fixed Rate Payable [Member] \| Cross Currency Swap One [Member]
Derivative [Line Items]
LIBOR fixed	1.10%
LIBOR rate receivable cap	3.50%

Face (par) amount of debt instrument at time of issuance.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant