Segment Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Segment Reporting Information [Line Items]
Net interest income	$ 75,557	$ 81,127
Reversal of Loan Losses Expensed	(2,500)
Provision for credit losses		1,410
Net interest income after provision for credit losses	78,057	79,717
Other income	7,705	(667)
Other expenses	15,015	14,561
Income before assessments	70,747	64,489
Affordable Housing Program assessments	7,237	6,796
Net income	63,510	57,693
Average assets	84,420,375	62,846,416
Total assets	86,729,035	61,976,215	81,562,150
Traditional Member Finance [Member]
Segment Reporting Information [Line Items]
Net interest income	48,605	51,683
Reversal of Loan Losses Expensed	0
Provision for credit losses		0
Net interest income after provision for credit losses	48,605	51,683
Other income	10,925	2,394
Other expenses	12,911	12,548
Income before assessments	46,619	41,529
Affordable Housing Program assessments	4,824	4,500
Net income	41,795	37,029
Average assets	77,016,706	54,847,679
Total assets	79,489,178	53,728,382
Mortgage Purchase Program [Member]
Segment Reporting Information [Line Items]
Net interest income	26,952	29,444
Reversal of Loan Losses Expensed	(2,500)
Provision for credit losses		1,410
Net interest income after provision for credit losses	29,452	28,034
Other income	(3,220)	(3,061)
Other expenses	2,104	2,013
Income before assessments	24,128	22,960
Affordable Housing Program assessments	2,413	2,296
Net income	21,715	20,664
Average assets	7,403,669	7,998,737
Total assets	$ 7,239,857	$ 8,247,833