Trading Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	$ 546,615	$ 122,404	$ 181,131
Trading Securities, Net Unrealized Gain (Loss)	783	140	606
U.S. government agency debentures
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	15,705	61,295	42,431
Trading Securities, Net Unrealized Gain (Loss)	(7)	(71)	(38)
U.S. government agency residential mortgage-backed securities
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	464,749	10,989	30,973
Trading Securities, Net Unrealized Gain (Loss)	876	17	195
Municipal and other tax-exempt securities
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	54,856	31,901	84,261
Trading Securities, Net Unrealized Gain (Loss)	(100)	210	421
Other trading securities
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	11,305	18,219	23,466
Trading Securities, Net Unrealized Gain (Loss)	$ 14	$ (16)	$ 28