Loans and Leases - Reserve for Loan and Lease Losses and Recorded Investment in Loans and Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	$ 88			$ 5
Ending balance: collectively evaluated for impairment	20,455			16,894
Total ending balance	20,543	$ 20,910	$ 17,499	16,899	$ 17,153	$ 17,628
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	31,810			38,979
Ending balance: collectively evaluated for impairment	2,857,157			2,167,396
Loans measured at fair value	2,014			2,234
Acquired non-credit impaired loans	594,561			967,177
Acquired credit impaired loans	1,622			14,575
Total Loans and Leases Held for Investment	3,487,164		3,285,886	3,190,361
Commercial, Financial and Agricultural [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	15			0
Ending balance: collectively evaluated for impairment	6,601			5,686
Total ending balance	6,616	8,313	7,037	5,686	5,788	6,418
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	7,883			10,273
Ending balance: collectively evaluated for impairment	774,886			587,901
Loans measured at fair value	0			0
Acquired non-credit impaired loans	75,983			184,784
Acquired credit impaired loans	465			722
Total Loans and Leases Held for Investment	859,217		823,266	783,680
Real Estate-Commercial and Construction [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	40			0
Ending balance: collectively evaluated for impairment	9,216			7,144
Total ending balance	9,256	8,468	7,505	7,144	7,549	6,572
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	17,274			23,014
Ending balance: collectively evaluated for impairment	1,307,585			950,730
Loans measured at fair value	2,014			2,234
Acquired non-credit impaired loans	344,818			525,944
Acquired credit impaired loans	356			12,451
Total Loans and Leases Held for Investment	1,672,047			1,514,373
Real Estate-Residential Secured for Business Purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	33			5
Ending balance: collectively evaluated for impairment	1,272			25
Total ending balance	1,305	1,129	774	30	56	763
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	4,471			4,614
Ending balance: collectively evaluated for impairment	209,340			127,096
Loans measured at fair value	0			0
Acquired non-credit impaired loans	95,625			155,348
Acquired credit impaired loans	584			1,136
Total Loans and Leases Held for Investment	310,020		294,068	288,194
Real Estate-Residential and Home Equity Secured for Personal Purpose [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0			0
Ending balance: collectively evaluated for impairment	1,715			1,549
Total ending balance	1,715	974	993	1,549	1,301	1,575
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	932			1,078
Ending balance: collectively evaluated for impairment	415,161			341,647
Loans measured at fair value	0			0
Acquired non-credit impaired loans	77,991			100,589
Acquired credit impaired loans	217			266
Total Loans and Leases Held for Investment	494,301			443,580
Loans to Individuals [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0			0
Ending balance: collectively evaluated for impairment	354			430
Total ending balance	354	329	364	430	411	346
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	0			0
Ending balance: collectively evaluated for impairment	27,297			30,137
Loans measured at fair value	0			0
Acquired non-credit impaired loans	144			512
Acquired credit impaired loans	0			0
Total Loans and Leases Held for Investment	27,441		30,373	30,649
Lease Financings [Member]
Reserve for loan and lease losses:
Ending balance: individually evaluated for impairment	0			0
Ending balance: collectively evaluated for impairment	1,290			1,163
Total ending balance	1,290	1,660	788	1,163	1,121	1,042
Loans and leases held for investment:
Ending balance: individually evaluated for impairment	1,250			0
Ending balance: collectively evaluated for impairment	122,888			129,885
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	124,138		134,739	129,885
Unallocated Financing Receivables [Member]
Reserve for loan and lease losses:
Ending balance: collectively evaluated for impairment	7			897
Total ending balance	$ 7	$ 37	$ 38	$ 897	$ 927	$ 912