Subsequent Events - Additional Information (Detail) (USD $)	12 Months Ended	1 Months Ended
May 31, 2013	May 31, 2012	May 31, 2011	Jun. 05, 2013 Subsequent Event
Subsequent Event [Line Items]
Dividends declared per share	$ 1.80	$ 0.80	$ 0.60	$ 0.20
Dividend payment date				Jul. 10, 2013
Dividend payment shareholders record date				Jun. 20, 2013

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

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=6959260&loc=d3e187085-122770

Name:	us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration