Cash Dividends (Details) (USD $)	12 Months Ended
Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Cash Dividends (Textual) [Abstract]
Total cash dividends per share (dollars per share)	$ 1.21	$ 1.09	$ 4.98
Special cash dividend per share (dollars per share)			$ 4.00bfb_SpecialCashDividendPerShare

Aggregate dividends paid 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=27012166&loc=d3e187085-122770

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