Loans and Allowance for Loan Losses - Disaggregated analysis of activity in the allowance for acquired credit impaired loans (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for loan losses:
Provision for loan losses before benefit attributable to FDIC loss share agreements	$ 11,890	$ 6,796	$ 5,078
Benefits attributable to FDIC loss share agreements		23	786
Total provision for loan losses charged to operations	11,890	6,819	5,864
Provision for loan losses recorded through the FDIC loss share receivable		(23)	(786)
Reduction due to loan removals	(821)	(899)	(3,407)
Loans:
Loans collectively evaluated for impairment	1,289
Non-acquired loans
Allowance for loan losses:
Provision for loan losses before benefit attributable to FDIC loss share agreements	8,684	5,539	2,930
Total provision for loan losses charged to operations	8,684	5,539	2,930
Loans individually evaluated for impairment	1,624	1,337	1,607
Loans collectively evaluated for impairment	41,824	35,623	32,483
Loans:
Loans individually evaluated for impairment	63,423	21,211	30,218
Loans collectively evaluated for impairment	6,428,732	5,219,830	4,190,508
Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	3,395	3,706	7,365
Provision for loan losses before benefit attributable to FDIC loss share agreements	2,053	588	(252)
Benefits attributable to FDIC loss share agreements		23	786
Total provision for loan losses charged to operations	2,053	611	534
Provision for loan losses recorded through the FDIC loss share receivable		(23)	(786)
Reduction due to loan removals	(821)	(899)	(3,407)
Balance at the end of the period	4,627	3,395	3,706
Loans collectively evaluated for impairment	4,627	3,395	3,706
Loans:
Loans collectively evaluated for impairment	623,430	605,941	737,576
Carrying value	623,430	605,941	737,576
Residential real estate
Loans:
Carrying value	260,787	258,100
Residential real estate | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	2,419	2,986	4,387
Provision for loan losses before benefit attributable to FDIC loss share agreements	1,662	(129)	99
Benefits attributable to FDIC loss share agreements		23	228
Total provision for loan losses charged to operations	1,662	(106)	327
Provision for loan losses recorded through the FDIC loss share receivable		(23)	(228)
Reduction due to loan removals	(528)	(438)	(1,500)
Balance at the end of the period	3,553	2,419	2,986
Loans collectively evaluated for impairment	3,553	2,419	2,986
Loans:
Loans collectively evaluated for impairment	260,787	258,100	313,319
Carrying value	260,787	258,100	313,319
Commercial non-owner occupied real estate | Construction and land development | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	1,408	(778)	(1,707)
Loans individually evaluated for impairment	1,063	348	615
Loans collectively evaluated for impairment	4,858	3,743	3,501
Loans:
Loans individually evaluated for impairment	43,230	3,033	6,280
Loans collectively evaluated for impairment	787,645	577,431	395,699
Commercial non-owner occupied real estate | Construction and land development | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	139	177	336
Provision for loan losses before benefit attributable to FDIC loss share agreements	163		(68)
Benefits attributable to FDIC loss share agreements			74
Total provision for loan losses charged to operations	163		6
Provision for loan losses recorded through the FDIC loss share receivable			(74)
Reduction due to loan removals	(122)	(38)	(91)
Balance at the end of the period	180	139	177
Loans collectively evaluated for impairment	180	139	177
Loans:
Loans collectively evaluated for impairment	49,649	44,373	54,272
Carrying value	49,649	44,373	54,272
Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	1,413	1,011	503
Loans individually evaluated for impairment	125	170	34
Loans collectively evaluated for impairment	6,400	4,810	3,534
Loans:
Loans individually evaluated for impairment	1,375	806	1,452
Loans collectively evaluated for impairment	1,007,518	713,909	486,325
Commercial non-owner occupied real estate | Other commercial non-owner occupied real estate | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	41	56	1,579
Provision for loan losses before benefit attributable to FDIC loss share agreements	247	1	(499)
Benefits attributable to FDIC loss share agreements			459
Total provision for loan losses charged to operations	247	1	(40)
Provision for loan losses recorded through the FDIC loss share receivable			(459)
Reduction due to loan removals		(16)	(1,024)
Balance at the end of the period	288	41	56
Loans collectively evaluated for impairment	288	41	56
Loans:
Loans collectively evaluated for impairment	234,595	218,821	268,058
Carrying value	234,595	218,821	268,058
Consumer real estate | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	558	313	275
Provision for loan losses before benefit attributable to FDIC loss share agreements	(83)	533	336
Benefits attributable to FDIC loss share agreements			(107)
Total provision for loan losses charged to operations	(83)	533	229
Provision for loan losses recorded through the FDIC loss share receivable			107
Reduction due to loan removals	(14)	(288)	(298)
Balance at the end of the period	461	558	313
Loans collectively evaluated for impairment	461	558	313
Loans:
Loans collectively evaluated for impairment	51,453	59,300	70,734
Carrying value	51,453	59,300	70,734
Consumer real estate | Home equity loans | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	159	791	403
Loans individually evaluated for impairment	135	40	3
Loans collectively evaluated for impairment	3,115	3,171	2,926
Loans:
Loans individually evaluated for impairment	3,011	1,674	309
Loans collectively evaluated for impairment	434,631	381,544	318,946
Commercial and industrial
Loans:
Carrying value	26,946	25,347
Commercial and industrial | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	1,079	1,452	(74)
Loans individually evaluated for impairment	15	386	279
Loans collectively evaluated for impairment	5,473	4,456	3,695
Loans:
Loans individually evaluated for impairment	1,156	1,263	1,487
Loans collectively evaluated for impairment	814,031	670,135	502,321
Commercial and industrial | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period	238	174	718
Provision for loan losses before benefit attributable to FDIC loss share agreements	64	183	(118)
Benefits attributable to FDIC loss share agreements			131
Total provision for loan losses charged to operations	64	183	13
Provision for loan losses recorded through the FDIC loss share receivable			(131)
Reduction due to loan removals	(157)	(119)	(426)
Balance at the end of the period	145	238	174
Loans collectively evaluated for impairment	145	238	174
Loans:
Loans collectively evaluated for impairment	26,946	25,347	31,193
Carrying value	26,946	25,347	31,193
Other income producing property | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	(201)	(501)	(252)
Loans individually evaluated for impairment	178	242	422
Loans collectively evaluated for impairment	1,197	1,300	1,541
Loans:
Loans individually evaluated for impairment	3,138	2,372	4,891
Loans collectively evaluated for impairment	190,709	175,866	170,957
Consumer
Loans:
Carrying value	51,453	59,300
Consumer | Non-acquired loans
Allowance for loan losses:
Total provision for loan losses charged to operations	3,010	3,310	2,890
Loans individually evaluated for impairment	7	4	3
Loans collectively evaluated for impairment	2,781	2,346	1,691
Loans:
Loans individually evaluated for impairment	239	145	102
Loans collectively evaluated for impairment	378,746	324,093	233,002
Consumer | Acquired credit impaired loans
Loans:
Carrying value	$ 51,453	$ 59,300
Single pay loans | Acquired credit impaired loans
Allowance for loan losses:
Balance at the beginning of the period			70
Provision for loan losses before benefit attributable to FDIC loss share agreements			(2)
Benefits attributable to FDIC loss share agreements			1
Total provision for loan losses charged to operations			(1)
Provision for loan losses recorded through the FDIC loss share receivable			(1)
Reduction due to loan removals			$ (68)