Loans and Leases - Reserve for Loan and Lease Losses and Recorded Investment in Loans and Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	$ 1,503		$ 732
Ending balance: collectively evaluated for impairment	30,092		22,388
Ending balance: acquired non-credit impaired loans evaluated for impairment	7		290
Total ending balance	31,602	$ 29,364	23,410	$ 21,555
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	26,002		41,840
Ending balance: collectively evaluated for impairment	3,687,577		3,146,843
Loans measured at fair value	1,748		1,895
Acquired non-credit impaired loans	351,859		497,785
Acquired credit impaired loans	693		1,525
Total Loans and Leases Held for Investment	4,067,879	4,006,574	3,689,888
Commercial, Financial and Agricultural [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	243		34
Ending balance: collectively evaluated for impairment	8,707		6,776
Ending balance: acquired non-credit impaired loans evaluated for impairment	0		132
Total ending balance	8,950	7,983	6,942	6,742
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	3,174		6,560
Ending balance: collectively evaluated for impairment	907,319		849,690
Loans measured at fair value	0		0
Acquired non-credit impaired loans	17,145		51,310
Acquired credit impaired loans	0		378
Total Loans and Leases Held for Investment	927,638	937,685	907,938
Real Estate-Commercial and Construction [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	925		684
Ending balance: collectively evaluated for impairment	14,049		10,378
Ending balance: acquired non-credit impaired loans evaluated for impairment	7		116
Total ending balance	14,981	13,903	11,178	9,839
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	18,467		30,573
Ending balance: collectively evaluated for impairment	1,772,999		1,441,709
Loans measured at fair value	1,748		1,895
Acquired non-credit impaired loans	222,749		295,420
Acquired credit impaired loans	206		356
Total Loans and Leases Held for Investment	2,016,169		1,769,953
Real Estate-Residential Secured for Business Purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0		14
Ending balance: collectively evaluated for impairment	2,302		1,815
Ending balance: acquired non-credit impaired loans evaluated for impairment	0		42
Total ending balance	2,302	2,236	1,871	1,661
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	1,232		2,173
Ending balance: collectively evaluated for impairment	303,342		249,015
Loans measured at fair value	0		0
Acquired non-credit impaired loans	55,923		81,587
Acquired credit impaired loans	425		586
Total Loans and Leases Held for Investment	360,922	362,796	333,361
Real Estate-Residential and Home Equity Secured for Personal Purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	335		0
Ending balance: collectively evaluated for impairment	3,044		1,908
Ending balance: acquired non-credit impaired loans evaluated for impairment	0		0
Total ending balance	3,379	3,199	1,908	1,754
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	3,129		1,284
Ending balance: collectively evaluated for impairment	530,946		449,827
Loans measured at fair value	0		0
Acquired non-credit impaired loans	55,901		69,325
Acquired credit impaired loans	62		205
Total Loans and Leases Held for Investment	590,038		520,641
Loans to Individuals [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0		0
Ending balance: collectively evaluated for impairment	469		372
Ending balance: acquired non-credit impaired loans evaluated for impairment	0		0
Total ending balance	469	484	372	373
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	0		0
Ending balance: collectively evaluated for impairment	32,462		28,112
Loans measured at fair value	0		0
Acquired non-credit impaired loans	141		143
Acquired credit impaired loans	0		0
Total Loans and Leases Held for Investment	32,603	32,759	28,255
Lease Financings [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0		0
Ending balance: collectively evaluated for impairment	1,275		1,079
Ending balance: acquired non-credit impaired loans evaluated for impairment	0		0
Total ending balance	1,275	1,288	1,079	1,132
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	0		1,250
Ending balance: collectively evaluated for impairment	140,509		128,490
Loans measured at fair value	0		0
Acquired non-credit impaired loans	0		0
Acquired credit impaired loans	0		0
Total Loans and Leases Held for Investment	140,509	141,956	129,740
Unallocated Financing Receivables [Member]
Reserve for loan and lease losses:
Ending balance: collectively evaluated for impairment	246		60
Ending balance: acquired non-credit impaired loans evaluated for impairment	0		0
Total ending balance	$ 246	$ 271	$ 60	$ 54