Investment Securities - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale and Held-to-Maturity Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Available-for-Sale Debt Securities
Amortized Cost	$ 1,909,483	$ 1,224,227
Gross Unrealized Gain	39,413	3,902
Gross Unrealized Loss	3,982	23,050
Available-for-sale securities	1,944,914	1,205,079
Held-to-Maturity Debt Securities
Amortized Cost	133,601	149,950
Gross Unrealized Gain	3,024
Gross Unrealized Loss	0
Fair Value	136,625	149,431
Equity Investments
Amortized Cost	23,856	17,218
Gross Unrealized Gain	46,190	20,015
Gross Unrealized Loss	0	0
Fair Value	70,046	37,233
State and political subdivisions
Held-to-Maturity Debt Securities
Amortized Cost	131,600	149,950
Gross Unrealized Gain	3,023	275
Gross Unrealized Loss	0	794
Fair Value	134,623	149,431
Equity Investments
Available for sale securities transfers to held to maturity unrealized gains	600	1,000
Foreign bonds
Held-to-Maturity Debt Securities
Amortized Cost	2,001
Gross Unrealized Gain	1
Gross Unrealized Loss	0
Fair Value	2,002
CMO
Available-for-Sale Debt Securities
Amortized Cost	336,194	376,867
Gross Unrealized Gain	4,578	1,721
Gross Unrealized Loss	542	6,838
Available-for-sale securities	340,230	371,750
FNMA MBS
Available-for-Sale Debt Securities
Amortized Cost	1,219,522	655,485
Gross Unrealized Gain	25,717	1,526
Gross Unrealized Loss	2,786	12,938
Available-for-sale securities	1,242,453	644,073
FHLMC MBS
Available-for-Sale Debt Securities
Amortized Cost	320,896	155,758
Gross Unrealized Gain	8,641	558
Gross Unrealized Loss	591	2,394
Available-for-sale securities	328,946	153,922
GNMA MBS
Available-for-Sale Debt Securities
Amortized Cost	32,871	36,117
Gross Unrealized Gain	477	97
Gross Unrealized Loss	63	880
Available-for-sale securities	33,285	35,334
Common Stock | Visa Class B shares
Equity Investments
Amortized Cost	15,716	13,918
Gross Unrealized Gain	45,565	20,015
Gross Unrealized Loss	0	0
Fair Value	61,281	33,933
Other equity investments
Equity Investments
Amortized Cost	8,140	3,300
Gross Unrealized Gain	625	0
Gross Unrealized Loss	0	0
Fair Value	$ 8,765	$ 3,300