Bank Line of Credit (Details) (USD $) In Millions	Jun. 30, 2011
Indemnity
Bank Line of Credit
Maximum borrowing capacity under the line of credit	$ 100
Fair value of bonds pledged as collateral on the line of credit	135
Exchange
Bank Line of Credit
Maximum borrowing capacity under the line of credit	200
Fair value of bonds pledged as collateral on the line of credit	$ 263