Short-Term Borrowings - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012
Short-term Debt [Line Items]
Federal funds interest rate	0.95%	0.95%
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Federal funds maturity date		1 day
Blanket Pledge [Member] \| FHLB [Member]
Short-term Debt [Line Items]
FHLB line of credit	$ 655.1	$ 481.8
Custody Pledge [Member] \| FHLB [Member]
Short-term Debt [Line Items]
FHLB line of credit	$ 29.4	$ 49.9

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

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