Accounts Payable and Other Accrued Liabilities (Details) (USD $) In Thousands	Jun. 30, 2011	Sep. 30, 2010
WGL Holdings, Inc.
Accounts payable - trade	$ 222,743	$ 193,776
Employee benefits and payroll accruals	20,044	24,078
Other accrued liabilities	39,407	7,508
Accounts Payable and Accrued Liabilities, Current, Total	282,194	225,362
Washington Gas Light Company
Accounts payable - trade	109,498	100,608
Employee benefits and payroll accruals	18,251	22,322
Other accrued liabilities	6,957	4,428
Accounts Payable and Accrued Liabilities, Current, Total	$ 134,706	$ 127,358