Securities Securities - Unrealized Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investment Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 17,785	$ 71,731
Investment securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	781,054	1,586,756
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	7,851	38,920
Investments with an Unrealized Loss of 12 months or longer, Fair Value	516,267	1,161,369
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	9,934	32,811
Total Investments with an Unrealized Loss, Fair Value	1,297,321	2,748,125
US Treasury Securities
Schedule of Investment Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	14	25
Investment securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	40,505	30,054
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	14	22
Investments with an Unrealized Loss of 12 months or longer, Fair Value	0	246
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	0	3
Total Investments with an Unrealized Loss, Fair Value	40,505	30,300
U.S. Government Agency Securities
Schedule of Investment Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	710	1,346
Investment securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	1,222	13,697
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	1	328
Investments with an Unrealized Loss of 12 months or longer, Fair Value	30,892	42,539
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	709	1,018
Total Investments with an Unrealized Loss, Fair Value	32,114	56,236
Mortgage-backed Agency Securities
Schedule of Investment Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	7,776	28,634
Investment securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	458,881	203,299
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	5,102	2,134
Investments with an Unrealized Loss of 12 months or longer, Fair Value	163,767	882,231
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	2,674	26,500
Total Investments with an Unrealized Loss, Fair Value	622,648	1,085,530
State and Municipal Securities
Schedule of Investment Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	7,249	34,858
Investment securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	204,958	1,044,757
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	1,938	30,780
Investments with an Unrealized Loss of 12 months or longer, Fair Value	244,884	198,610
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	5,311	4,078
Total Investments with an Unrealized Loss, Fair Value	449,842	1,243,367
Asset-backed Securities
Schedule of Investment Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	1,293	4,345
Investment securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	75,488	268,677
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	796	4,118
Investments with an Unrealized Loss of 12 months or longer, Fair Value	59,816	11,828
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	497	227
Total Investments with an Unrealized Loss, Fair Value	135,304	280,505
Corporate Notes
Schedule of Investment Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	743	2,523
Investment securities, continuous unrealized loss position [Abstract]
Investments with an Unrealized Loss of less than 12 months, Fair Value	0	26,272
Investments with an Unrealized Loss of less than 12 months, Unrealized Losses	0	1,538
Investments with an Unrealized Loss of 12 months or longer, Fair Value	16,908	25,915
Investments with an Unrealized Loss of 12 months or longer, Unrealized Losses	743	985
Total Investments with an Unrealized Loss, Fair Value	$ 16,908	$ 52,187