Notes Receivable - Additional Information (Detail) (USD $)	3 Months Ended	6 Months Ended
Jun. 30, 2013 Receivables	Jun. 30, 2012	Jun. 30, 2013 Receivables	Jun. 30, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of notes receivable	2		2
Interest income	$ 3,052,000	$ 3,021,000	$ 6,103,000	$ 6,175,000
Payment received relating to notes receivables			3,500,000	6,600,000
National Bonds [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Interest income	$ 3,100,000	$ 2,900,000	$ 6,100,000	$ 6,100,000

The cash inflow associated with the collection, including prepayments, of loans receivable issued for financing of goods and services.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 12

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585

Name:	us-gaap_ProceedsFromCollectionOfLoansReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration