Securities - Trading Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of fair value of trading securities
Trading Securities	$ 634,197	$ 730,685
Investment-related Liabilities
Securities sold, not yet purchased, at fair value	251,581	232,821
US Treasury Securities
Schedule of fair value of trading securities
Trading Securities	1,033
Bonds
Schedule of fair value of trading securities
Trading Securities	57,996	52,078
Residential mortgage-backed Securities
Schedule of fair value of trading securities
Trading Securities	338,892	372,817
Commercial mortgage-backed securities
Schedule of fair value of trading securities
Trading Securities	8,664	6,125
Collateralized mortgage obligations
Schedule of fair value of trading securities
Trading Securities	1	5,122
Corporate securities
Schedule of fair value of trading securities
Trading Securities	80,361	96,182
States and political subdivisions
Schedule of fair value of trading securities
Trading Securities	112,646	170,413
Unit investment trusts
Schedule of fair value of trading securities
Trading Securities	27,480	22,612
Private-label securitized product
Schedule of fair value of trading securities
Trading Securities	3,684	1,631
Other
Schedule of fair value of trading securities
Trading Securities	$ 3,440	$ 3,705