Trading Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	$ 677,156	$ 337,628	$ 279,539
Trading Securities, Net Unrealized Gain (Loss)	1,708	738	1,545
U.S. government agency debentures
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	18,365	6,234	59,733
Trading Securities, Net Unrealized Gain (Loss)	(74)	(4)	71
U.S. government agency residential mortgage-backed securities
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	578,977	310,067	146,896
Trading Securities, Net Unrealized Gain (Loss)	1,575	635	821
Municipal and other tax-exempt securities
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	45,114	14,427	58,797
Trading Securities, Net Unrealized Gain (Loss)	171	50	546
Other trading securities
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	34,700	6,900	14,113
Trading Securities, Net Unrealized Gain (Loss)	$ 36	$ 57	$ 107