Borrowings - Lines of Credit Under Formal Agreements (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
M&T (Consolidated) [Member]
Schedule Of Borrowings [Line Items]
Outstanding borrowings
Unused	30,000
M&T Bank [Member]
Schedule Of Borrowings [Line Items]
Outstanding borrowings	29,586
Unused	21,127,615
Wilmington Trust, N.A. [Member]
Schedule Of Borrowings [Line Items]
Outstanding borrowings
Unused	$ 309,658

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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