Changes in Level 3 Assets (Parenthetical) (Detail) (Auction Rate Securities, Redemptions by Issuers, USD $) In Millions, unless otherwise specified	6 Months Ended
Jun. 30, 2013
Auction Rate Securities \| Redemptions by Issuers
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Realized gains (losses) on securities	$ 0.1

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 9

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27357-111563

Name:	us-gaap_AvailableForSaleSecuritiesGrossRealizedGainLossNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration