Affordable Housing Program (AHP) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Affordable Housing Program [Roll Forward]
AHP Obligation, Beginning Balance			$ 104,883
AHP, Expense (Current Year Additions)	$ 9,690	$ 6,936	16,986	$ 13,333
AHP, Subsidy Uses, Net			(14,548)	$ (19,620)
AHP Obligation, Ending Balance	$ 107,321		$ 107,321