Investment Securities - Schedule of Investment Securities' Gross Unrealized Losses and Fair Value by Investment Category (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair Value	$ 73,219	$ 398,776
Available-for-sale debt securities, Less than 12 months, Unrealized Loss	302	3,624
Available-for-sale debt securities, 12 months or longer, Fair Value	718,120	239,678
Available-for-sale debt securities, 12 months or longer, Unrealized Loss	22,748	8,024
Available-for-sale debt securities, Total, Fair Value	791,339	638,454
Available-for-sale debt securities, Total, Unrealized Loss	23,050	11,648
Held-to-maturity debt securities:
Held-to-maturity, Less than 12 months, Fair Value	91,228	23,404
Held-to-maturity, Less than 12 months, Unrealized Loss	155	59
Held-to-maturity, 12 months or longer, Fair Value	58,203	5,625
Held-to-maturity, 12 months or longer, Unrealized Loss	639	32
Held-to-maturity, Total, Fair Value	149,431	29,029
Held-to-maturity, Total, Unrealized Loss	794	91
State and political subdivisions
Held-to-maturity debt securities:
Held-to-maturity, Less than 12 months, Fair Value	91,228	23,404
Held-to-maturity, Less than 12 months, Unrealized Loss	155	59
Held-to-maturity, 12 months or longer, Fair Value	58,203	5,625
Held-to-maturity, 12 months or longer, Unrealized Loss	639	32
Held-to-maturity, Total, Fair Value	149,431	29,029
Held-to-maturity, Total, Unrealized Loss	794	91
CMO
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair Value	17,143	146,726
Available-for-sale debt securities, Less than 12 months, Unrealized Loss	40	1,820
Available-for-sale debt securities, 12 months or longer, Fair Value	212,208	77,149
Available-for-sale debt securities, 12 months or longer, Unrealized Loss	6,798	2,321
Available-for-sale debt securities, Total, Fair Value	229,351	223,875
Available-for-sale debt securities, Total, Unrealized Loss	6,838	4,141
FNMA MBS
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair Value	34,214	204,921
Available-for-sale debt securities, Less than 12 months, Unrealized Loss	162	1,479
Available-for-sale debt securities, 12 months or longer, Fair Value	407,638	126,342
Available-for-sale debt securities, 12 months or longer, Unrealized Loss	12,776	4,693
Available-for-sale debt securities, Total, Fair Value	441,852	331,263
Available-for-sale debt securities, Total, Unrealized Loss	12,938	6,172
FHLMC MBS
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair Value	16,025	42,514
Available-for-sale debt securities, Less than 12 months, Unrealized Loss	21	269
Available-for-sale debt securities, 12 months or longer, Fair Value	76,469	21,405
Available-for-sale debt securities, 12 months or longer, Unrealized Loss	2,373	655
Available-for-sale debt securities, Total, Fair Value	92,494	63,919
Available-for-sale debt securities, Total, Unrealized Loss	2,394	924
GNMA MBS
Available-for-sale debt securities:
Available-for-sale debt securities, Less than 12 months, Fair Value	5,837	4,615
Available-for-sale debt securities, Less than 12 months, Unrealized Loss	79	56
Available-for-sale debt securities, 12 months or longer, Fair Value	21,805	14,782
Available-for-sale debt securities, 12 months or longer, Unrealized Loss	801	355
Available-for-sale debt securities, Total, Fair Value	27,642	19,397
Available-for-sale debt securities, Total, Unrealized Loss	$ 880	411
Other equity investments
Other equity investments
Other investments, Less than 12 months, Fair Value		0
Other investments, Less than 12 months, Unrealized Loss		0
Other investments, 12 months or longer, Fair Value		624
Other investments, 12 months or longer, Unrealized Loss		20
Other investments, Total, Fair Value		624
Other investments, Total, Unrealized Loss		$ 20