LOANS - Age Analysis of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	$ 19,530	$ 40,095
90 Days or More Past Due	4,825	375
Total loans past due and still accruing	24,355	40,470
Nonaccrual	62,121	57,338
Purchased Credit Impaired	7,037	15,965
Current	3,269,841	3,076,712
Total loans held for investment	3,363,354	3,190,485	$ 3,071,761
Originated
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	15,338	36,969
90 Days or More Past Due	2,903	375
Total loans past due and still accruing	18,241	37,344
Nonaccrual	57,855	51,860
Purchased Credit Impaired	0	0
Current	2,998,478	2,587,287
Total loans held for investment	3,074,574	2,676,491	2,485,239
Acquired
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	4,192	3,126
90 Days or More Past Due	1,922	0
Total loans past due and still accruing	6,114	3,126
Nonaccrual	4,266	5,478
Purchased Credit Impaired	7,037	15,965
Current	271,363	489,425
Total loans held for investment	288,780	513,994	586,522
Commercial & industrial
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans held for investment	1,142,733	1,066,266
Commercial & industrial | Originated
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	10,960	15,917
90 Days or More Past Due	2,413	242
Total loans past due and still accruing	13,373	16,159
Nonaccrual	35,824	45,413
Purchased Credit Impaired	0	0
Current	1,065,270	941,225
Total loans held for investment	1,114,467	1,002,797
Commercial & industrial | Acquired
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	0	0
90 Days or More Past Due	0	0
Total loans past due and still accruing	0	0
Nonaccrual	1,795	1,901
Purchased Credit Impaired	1,563	3,237
Current	24,908	58,331
Total loans held for investment	28,266	63,469	82,135
Mortgage warehouse
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans held for investment	236,307	220,230
Mortgage warehouse | Originated
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	0	0
90 Days or More Past Due	0	0
Total loans past due and still accruing	0	0
Nonaccrual	0	0
Purchased Credit Impaired	0	0
Current	236,307	220,230
Total loans held for investment	236,307	220,230
Mortgage warehouse | Acquired
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans held for investment	0	0
Owner occupied commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans held for investment	435,667	415,230
Owner occupied commercial real estate | Originated
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	428	1,109
90 Days or More Past Due	0	0
Total loans past due and still accruing	428	1,109
Nonaccrual	3,494	0
Purchased Credit Impaired	0	0
Current	378,964	326,797
Total loans held for investment	382,886	327,906	312,162
Owner occupied commercial real estate | Acquired
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	778	233
90 Days or More Past Due	0	0
Total loans past due and still accruing	778	233
Nonaccrual	1,671	1,886
Purchased Credit Impaired	14	4,062
Current	50,318	81,143
Total loans held for investment	52,781	87,324	96,236
Commercial real estate
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans held for investment	1,133,427	1,067,779
Commercial real estate | Originated
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	1,201	16,250
90 Days or More Past Due	0	0
Total loans past due and still accruing	1,201	16,250
Nonaccrual	13,379	0
Purchased Credit Impaired	0	0
Current	999,347	807,111
Total loans held for investment	1,013,927	823,361	806,327
Commercial real estate | Acquired
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	1,942	1,885
90 Days or More Past Due	976	0
Total loans past due and still accruing	2,918	1,885
Nonaccrual	0	312
Purchased Credit Impaired	3,594	6,437
Current	112,988	235,784
Total loans held for investment	119,500	244,418	262,415
Construction, land & land development
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans held for investment	153,257	164,952
Construction, land & land development | Originated
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	1,622	2,255
90 Days or More Past Due	0	133
Total loans past due and still accruing	1,622	2,388
Nonaccrual	1,457	3,287
Purchased Credit Impaired	0	0
Current	134,555	131,323
Total loans held for investment	137,634	136,998	146,522
Construction, land & land development | Acquired
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	0	204
90 Days or More Past Due	0	0
Total loans past due and still accruing	0	204
Nonaccrual	695	714
Purchased Credit Impaired	0	0
Current	14,928	27,036
Total loans held for investment	15,623	27,954	47,334
Residential mortgage
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans held for investment	249,046	238,580
Residential mortgage | Originated
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	943	1,311
90 Days or More Past Due	490	0
Total loans past due and still accruing	1,433	1,311
Nonaccrual	3,658	3,111
Purchased Credit Impaired	0	0
Current	172,077	144,599
Total loans held for investment	177,168	149,021	138,095
Residential mortgage | Acquired
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	1,425	804
90 Days or More Past Due	946	0
Total loans past due and still accruing	2,371	804
Nonaccrual	101	454
Purchased Credit Impaired	1,866	2,229
Current	67,540	86,072
Total loans held for investment	71,878	89,559	96,994
Consumer and other
Financing Receivable, Recorded Investment, Aging [Abstract]
Total loans held for investment	12,917	17,448
Consumer and other | Originated
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	184	127
90 Days or More Past Due	0	0
Total loans past due and still accruing	184	127
Nonaccrual	43	49
Purchased Credit Impaired	0	0
Current	11,958	16,002
Total loans held for investment	12,185	16,178	15,418
Consumer and other | Acquired
Financing Receivable, Recorded Investment, Aging [Abstract]
30 - 89 Days Past Due	47	0
90 Days or More Past Due	0	0
Total loans past due and still accruing	47	0
Nonaccrual	4	211
Purchased Credit Impaired	0	0
Current	681	1,059
Total loans held for investment	$ 732	$ 1,270	$ 1,408