Trading Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Schedule of Trading Securities [Line Items]
Trading securities	$ 1,956,923	$ 462,676
Trading Securities, Net Unrealized Gain (Loss)	10,969	(448)
U.S. government agency debentures [Member]
Schedule of Trading Securities [Line Items]
Trading securities	63,765	21,196
Trading Securities, Net Unrealized Gain (Loss)	254	8
U.S. government agency residential mortgage-backed securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	1,791,584	392,673
Trading Securities, Net Unrealized Gain (Loss)	9,966	(517)
Municipal and other tax-exempt securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	34,507	13,559
Trading Securities, Net Unrealized Gain (Loss)	(1)	83
Asset-backed securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	42,656	23,885
Trading Securities, Net Unrealized Gain (Loss)	685	(26)
Other trading securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	24,411	11,363
Trading Securities, Net Unrealized Gain (Loss)	$ 65	$ 4