Segment Information Financial Performance (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($) Segment	Jun. 30, 2016 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments | Segment			2
Net interest income	$ 105,768	$ 82,610	$ 209,041	$ 171,455
Non-interest income (loss)	10,056	6,615	(657)	2,427
Non-interest expense	19,540	20,896	39,606	42,647
Income before assessments	96,284	68,329	168,778	131,235
Affordable Housing Program assessments	9,690	6,936	16,986	13,333
Net income	86,594	61,393	151,792	117,902
Traditional Member Finance [Member]
Segment Reporting Information [Line Items]
Net interest income	82,116	66,533	161,990	135,714
Non-interest income (loss)	10,639	6,207	1,074	1,042
Non-interest expense	16,980	18,279	34,120	37,250
Income before assessments	75,775	54,461	128,944	99,506
Affordable Housing Program assessments	7,639	5,549	13,002	10,160
Net income	68,136	48,912	115,942	89,346
Mortgage Purchase Program [Member]
Segment Reporting Information [Line Items]
Net interest income	23,652	16,077	47,051	35,741
Non-interest income (loss)	(583)	408	(1,731)	1,385
Non-interest expense	2,560	2,617	5,486	5,397
Income before assessments	20,509	13,868	39,834	31,729
Affordable Housing Program assessments	2,051	1,387	3,984	3,173
Net income	$ 18,458	$ 12,481	$ 35,850	$ 28,556