Trading Securities (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	$ 118,044	$ 188,700	$ 86,571
Trading Securities, Net Unrealized Gain (Loss)	94	187	136
U.S. Government agency debentures [Member]
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	26,283	85,092	28,588
Trading Securities, Net Unrealized Gain (Loss)	40	(62)	14
U.S. agency residential mortgage-backed securities [Member]
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	17,179	31,199	23,595
Trading Securities, Net Unrealized Gain (Loss)	5	269	83
Municipal and other tax-exempt securities [Member]
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	54,164	38,951	27,280
Trading Securities, Net Unrealized Gain (Loss)	(4)	18	58
Other trading securities [Member]
Schedule of Trading Securities [Line Items]
Trading Securities, Fair Value	20,418	33,458	7,108
Trading Securities, Net Unrealized Gain (Loss)	$ 53	$ (38)	$ (19)