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, 2018	Dec. 31, 2017
Available-for-Sale Debt Securities
Amortized Cost	$ 1,224,227	$ 847,791
Gross Unrealized Gain	3,902	1,356
Gross Unrealized Loss	23,050	11,648
Fair Value	1,205,079	837,499
Held-to-Maturity Debt Securities
Amortized Cost	149,950	161,186
Fair Value	149,431	162,853
Equity Investments
Amortized Cost	17,218	643
Gross Unrealized Gain	20,015	0
Gross Unrealized Loss	0	20
Fair Value	37,233	623
State and political subdivisions
Held-to-Maturity Debt Securities
Amortized Cost	149,950	161,186
Gross Unrealized Gain	275	1,758
Gross Unrealized Loss	794	91
Fair Value	149,431	162,853
Equity Investments
Available for sale securities transfers to held to maturity unrealized gains	1,000	1,600
CMO
Available-for-Sale Debt Securities
Amortized Cost	376,867	250,592
Gross Unrealized Gain	1,721	88
Gross Unrealized Loss	6,838	4,141
Fair Value	371,750	246,539
FNMA MBS
Available-for-Sale Debt Securities
Amortized Cost	655,485	479,218
Gross Unrealized Gain	1,526	941
Gross Unrealized Loss	12,938	6,172
Fair Value	644,073	473,987
FHLMC MBS
Available-for-Sale Debt Securities
Amortized Cost	155,758	88,681
Gross Unrealized Gain	558	118
Gross Unrealized Loss	2,394	924
Fair Value	153,922	87,875
GNMA MBS
Available-for-Sale Debt Securities
Amortized Cost	36,117	29,300
Gross Unrealized Gain	97	209
Gross Unrealized Loss	880	411
Fair Value	35,334	29,098
Common Stock | Visa | Visa Class B shares
Equity Investments
Amortized Cost	13,918
Gross Unrealized Gain	20,015
Gross Unrealized Loss	0
Fair Value	33,933
Other equity investments
Equity Investments
Amortized Cost	3,300	643
Gross Unrealized Gain	0	0
Gross Unrealized Loss	0	20
Fair Value	$ 3,300	$ 623