Securities Securities - Available for sale (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	$ 3,491,633	$ 3,146,023
Gross Unrealized Gain	66,147	5,275
Gross Unrealized Loss	17,785	67,612
Securities available-for-sale, at fair value	3,539,995	3,083,686
Available-for-sale, Amortized Cost
Due in one year of less	72,914
Due in one year to five years	12,879
Due in five to ten years	103,099
Due after ten years	1,689,884
Mortgage-backed securities	1,458,894
Asset-backed securities	153,963
Amortized Cost	3,491,633
Available-for-sale, Fair Value
Due in one year or less	72,916
Due in one year to five years	13,083
Due in five years to ten years	103,584
Due after ten years	1,733,533
Mortgage-backed securities	1,463,907
Asset-backed securities	152,972
Securities available-for-sale, at fair value	3,539,995	3,083,686
State and Municipal Securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,669,606	1,259,267
Gross Unrealized Gain	52,096	1,126
Gross Unrealized Loss	7,249	30,739
Securities available-for-sale, at fair value	1,714,453	1,229,654
Available-for-sale, Fair Value
Securities available-for-sale, at fair value	1,714,453	1,229,654
U.S. Government Agency Securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	80,096	71,456
Gross Unrealized Gain	306	49
Gross Unrealized Loss	710	1,346
Securities available-for-sale, at fair value	79,692	70,159
Available-for-sale, Fair Value
Securities available-for-sale, at fair value	79,692	70,159
Mortgage-backed Agency Securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	1,458,894	1,336,469
Gross Unrealized Gain	12,789	3,110
Gross Unrealized Loss	7,776	28,634
Securities available-for-sale, at fair value	1,463,907	1,310,945
Available-for-sale, Fair Value
Securities available-for-sale, at fair value	1,463,907	1,310,945
US Treasury Securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	72,862	30,325
Gross Unrealized Gain	19	0
Gross Unrealized Loss	14	25
Securities available-for-sale, at fair value	72,867	30,300
Available-for-sale, Fair Value
Securities available-for-sale, at fair value	72,867	30,300
Asset-backed Securities
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	153,963	379,107
Gross Unrealized Gain	302	820
Gross Unrealized Loss	1,293	4,345
Securities available-for-sale, at fair value	152,972	375,582
Available-for-sale, Fair Value
Securities available-for-sale, at fair value	152,972	375,582
Corporate Notes
Debt Securities, Available-for-sale [Abstract]
Amortized Cost	56,212	69,399
Gross Unrealized Gain	635	170
Gross Unrealized Loss	743	2,523
Securities available-for-sale, at fair value	56,104	67,046
Available-for-sale, Fair Value
Securities available-for-sale, at fair value	$ 56,104	$ 67,046