Statement of Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Retained Earnings, Unrestricted [Member]	Retained Earnings, Restricted [Member]	Retained Earnings, Total [Member]	Accumulated Other Comprehensive Loss [Member]
Shares, Issued beginning balance at Dec. 31, 2015		44,288
Beginning balance at Dec. 31, 2015	$ 5,153,125	$ 4,428,756	$ 530,998	$ 206,648	$ 737,646	$ (13,277)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from sale of capital stock, shares		356
Proceeds from sale of capital stock, par value	35,663	$ 35,663
Net shares reclassified to mandatorily redeemable capital stock, shares		(2,379)
Net shares reclassified to mandatorily redeemable capital stock, par value	(237,883)	$ (237,883)
Comprehensive Income	119,069		94,322	23,580	117,902	1,167
Cash dividends on capital stock	(86,969)		(86,969)		(86,969)
Shares, Issued ending balance at Jun. 30, 2016		42,265
Ending balance at Jun. 30, 2016	4,983,005	$ 4,226,536	538,351	230,228	768,579	(12,110)
Shares, Issued beginning balance at Dec. 31, 2016		41,569
Beginning balance at Dec. 31, 2016	4,978,095	$ 4,156,944	574,122	260,285	834,407	(13,256)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Proceeds from sale of capital stock, shares		2,502
Proceeds from sale of capital stock, par value	250,196	$ 250,196
Net shares reclassified to mandatorily redeemable capital stock, shares		(1,874)
Net shares reclassified to mandatorily redeemable capital stock, par value	(187,405)	$ (187,405)
Comprehensive Income	152,626		121,433	30,359	151,792	834
Cash dividends on capital stock	(95,629)		(95,629)		(95,629)
Shares, Issued ending balance at Jun. 30, 2017		42,197
Ending balance at Jun. 30, 2017	$ 5,097,883	$ 4,219,735	$ 599,926	$ 290,644	$ 890,570	$ (12,422)