Securities - Trading Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of fair value of trading securities
Trading Securities	$ 660,314	$ 730,685
Investment-related Liabilities
Securities sold, not yet purchased, at fair value	179,582	232,821
US Treasury Securities
Schedule of fair value of trading securities
Trading Securities	2,328
Bonds
Schedule of fair value of trading securities
Trading Securities	30,223	52,078
Residential mortgage-backed Securities
Schedule of fair value of trading securities
Trading Securities	360,091	372,817
Commercial mortgage-backed securities
Schedule of fair value of trading securities
Trading Securities	5,781	6,125
Collateralized mortgage obligations
Schedule of fair value of trading securities
Trading Securities	35,708	5,122
Corporate securities
Schedule of fair value of trading securities
Trading Securities	74,249	96,182
States and political subdivisions
Schedule of fair value of trading securities
Trading Securities	119,751	170,413
Unit investment trusts
Schedule of fair value of trading securities
Trading Securities	24,013	22,612
Private-label securitized product
Schedule of fair value of trading securities
Trading Securities	4,806	1,631
Other
Schedule of fair value of trading securities
Trading Securities	$ 3,364	$ 3,705