Subsequent Events - Additional Information (Detail) (Subsequent Event [Member], USD $)	6 Months Ended	1 Months Ended
Jun. 30, 2013	Jul. 09, 2013 Class A Shares [Member]
Subsequent Event [Line Items]
Shares issued in exchange for vested RSUs		89,328
Cash dividend distribution	$ 1.32
Dividend declared date	Aug. 08, 2013
Dividend payment date	Aug. 30, 2013
Dividend record date	Aug. 26, 2013

Number of shares of equity interests issued or issuable to acquire entity.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)(4)

-URI http://asc.fasb.org/extlink&oid=7488404&loc=d3e6927-128479

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- Definition

Aggregate dividends paid during the period for each share of common stock outstanding.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

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- Definition

Date the declared dividend will be paid, in CCYY-MM-DD format.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

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- Definition

Date the dividend to be paid was declared, in CCYY-MM-DD format.

+ References

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- Definition

Date the holder must own the stock to be entitled to the dividend, in CCYY-MM-DD format.

+ References

No definition available.

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