Revolving Credit Facility (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Line of Credit Facility [Abstract]
Revolving credit facility	$ 0	$ 0
Outstanding letters of credit	$ 7,200,000	$ 6,400,000

Amount borrowed under the credit facility as of the balance sheet date.

Reference 1: 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_LineOfCreditFacilityAmountOutstanding
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant