Segment Information Asset Balances (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Total assets	$ 109,052,805	$ 104,635,281
Traditional Member Finance [Member]
Segment Reporting Information [Line Items]
Total assets	98,533,598	95,456,372
Mortgage Purchase Program [Member]
Segment Reporting Information [Line Items]
Total assets	$ 10,519,207	$ 9,178,909