Trading Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Schedule of Trading Securities [Line Items]
Trading securities	$ 2,140,326	$ 1,956,923
Trading Securities, Net Unrealized Gain (Loss)	12,898	10,969
U.S. government agency debentures [Member]
Schedule of Trading Securities [Line Items]
Trading securities	51,576	63,765
Trading Securities, Net Unrealized Gain (Loss)	52	254
Residential agency mortgage-backed securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	1,952,742	1,791,584
Trading Securities, Net Unrealized Gain (Loss)	12,377	9,966
Municipal and other tax-exempt securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	50,637	34,507
Trading Securities, Net Unrealized Gain (Loss)	225	(1)
Asset-backed securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	40,890	42,656
Trading Securities, Net Unrealized Gain (Loss)	128	685
Other debt securities [Member]
Schedule of Trading Securities [Line Items]
Trading securities	44,481	24,411
Trading Securities, Net Unrealized Gain (Loss)	$ 116	$ 65