Securities - Trading Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of fair value of trading securities
Trading Securities	$ 756,151	$ 730,685
Investment-related Liabilities
Securities sold, not yet purchased, at fair value	255,551	232,821
US Treasury Securities
Schedule of fair value of trading securities
Trading Securities	751
Bonds
Schedule of fair value of trading securities
Trading Securities	51,229	52,078
Residential mortgage-backed Securities
Schedule of fair value of trading securities
Trading Securities	430,889	372,817
Commercial mortgage-backed securities
Schedule of fair value of trading securities
Trading Securities	8,962	6,125
Collateralized mortgage obligations
Schedule of fair value of trading securities
Trading Securities	12,907	5,122
Corporate securities
Schedule of fair value of trading securities
Trading Securities	83,233	96,182
States and political subdivisions
Schedule of fair value of trading securities
Trading Securities	114,421	170,413
Unit investment trusts
Schedule of fair value of trading securities
Trading Securities	47,767	22,612
Private-label securitized product
Schedule of fair value of trading securities
Trading Securities	2,525	1,631
Other
Schedule of fair value of trading securities
Trading Securities	$ 3,467	$ 3,705