Trading Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Trading Securities [Line Items]
Trading securities	$ 1,900,395	$ 1,956,923
Trading Securities, Net Unrealized Gain (Loss)	8,626	10,969
U.S. government agency debentures [Member]
Schedule of Trading Securities [Line Items]
Trading securities	83,148	63,765
Trading Securities, Net Unrealized Gain (Loss)	127	254
Residential agency mortgage-backed securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	1,620,613	1,791,584
Trading Securities, Net Unrealized Gain (Loss)	7,558	9,966
Municipal and other tax-exempt securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	49,718	34,507
Trading Securities, Net Unrealized Gain (Loss)	191	(1)
Asset-backed securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	93,546	42,656
Trading Securities, Net Unrealized Gain (Loss)	548	685
Other debt securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	53,370	24,411
Trading Securities, Net Unrealized Gain (Loss)	$ 202	$ 65