Fair Value Measurements (Details 2) (Recurring [Member], Level 3 [Member], Failed Auction Securities [Member], USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2012
Recurring [Member] \| Level 3 [Member] \| Failed Auction Securities [Member]
Change in the estimated fair values calculated for those assets valued on a recurring basis utilizing Level 3 inputs
Balance at the beginning of the period	$ 7,472
Redemptions, at par	(3,000)
Credit gains on available for-sale-securities included in Other income (expense), net	16
Unrealized gain included in Other comprehensive income (loss)	561
Balance at the end of the period	$ 5,049

This item represents the amount of the total change in unrealized (holding) gains or losses for the period which are included in the statement of income (or changes in net assets) in other income. Such unrealized (holding) gains or losses relate to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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