LOANS - Risk category (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2017 USD ($) region	Dec. 31, 2016 USD ($)
Risk category
Number of main regions | region	4
Total loans	$ 3,184,063	$ 2,319,976
Non-PCI loans
Risk category
Total loans	3,154,055	2,291,720
Non-PCI loans | Commercial loan portfolio
Risk category
Total loans	2,196,456	1,583,380
Non-PCI loans | Commercial loan portfolio | Acceptable credit quality
Risk category
Total loans	2,120,171	1,511,506
Non-PCI loans | Commercial loan portfolio | Special mention
Risk category
Total loans	23,945	19,665
Non-PCI loans | Commercial loan portfolio | Substandard
Risk category
Total loans	24,460	34,277
Non-PCI loans | Commercial loan portfolio | Substandard - nonaccrual
Risk category
Total loans	19,266	10,725
Non-PCI loans | Commercial loan portfolio | Not graded
Risk category
Total loans	8,614	7,207
Non-PCI loans | Other loan portfolio
Risk category
Total loans	957,599	708,340
Non-PCI loans | Other loan portfolio | Performing
Risk category
Total loans	950,997	701,767
Non-PCI loans | Other loan portfolio | Impaired
Risk category
Total loans	6,602	6,573
Commercial | Commercial loan portfolio
Risk category
Total loans	571,111	457,827
Commercial | Non-PCI loans | Commercial loan portfolio
Risk category
Total loans	568,855	454,310
Commercial | Non-PCI loans | Commercial loan portfolio | Acceptable credit quality
Risk category
Total loans	540,150	426,560
Commercial | Non-PCI loans | Commercial loan portfolio | Special mention
Risk category
Total loans	15,702	10,930
Commercial | Non-PCI loans | Commercial loan portfolio | Substandard
Risk category
Total loans	9,777	12,649
Commercial | Non-PCI loans | Commercial loan portfolio | Substandard - nonaccrual
Risk category
Total loans	2,989	3,559
Commercial | Non-PCI loans | Commercial loan portfolio | Not graded
Risk category
Total loans	237	612
Commercial real estate | Commercial loan portfolio
Risk category
Total loans	1,470,487	969,615
Commercial real estate | Non-PCI loans | Commercial loan portfolio
Risk category
Total loans	1,456,072	963,895
Commercial real estate | Non-PCI loans | Commercial loan portfolio | Acceptable credit quality
Risk category
Total loans	1,415,774	925,244
Commercial real estate | Non-PCI loans | Commercial loan portfolio | Special mention
Risk category
Total loans	8,243	8,735
Commercial real estate | Non-PCI loans | Commercial loan portfolio | Substandard
Risk category
Total loans	14,473	21,178
Commercial real estate | Non-PCI loans | Commercial loan portfolio | Substandard - nonaccrual
Risk category
Total loans	16,277	7,145
Commercial real estate | Non-PCI loans | Commercial loan portfolio | Not graded
Risk category
Total loans	1,305	1,593
Construction and land development | Commercial loan portfolio
Risk category
Total loans	176,098	177,325
Construction and land development | Non-PCI loans | Commercial loan portfolio
Risk category
Total loans	171,529	165,175
Construction and land development | Non-PCI loans | Commercial loan portfolio | Acceptable credit quality
Risk category
Total loans	164,247	159,702
Construction and land development | Non-PCI loans | Commercial loan portfolio | Substandard
Risk category
Total loans	210	450
Construction and land development | Non-PCI loans | Commercial loan portfolio | Substandard - nonaccrual
Risk category
Total loans		21
Construction and land development | Non-PCI loans | Commercial loan portfolio | Not graded
Risk category
Total loans	7,072	5,002
Residential real estate | Other loan portfolio
Risk category
Total loans	428,464	253,713
Residential real estate | Non-PCI loans | Other loan portfolio
Risk category
Total loans	419,905	247,156
Residential real estate | Non-PCI loans | Other loan portfolio | Performing
Risk category
Total loans	414,409	242,127
Residential real estate | Non-PCI loans | Other loan portfolio | Impaired
Risk category
Total loans	5,496	5,029
Consumer | Other loan portfolio
Risk category
Total loans	335,902	270,017
Consumer | Non-PCI loans | Other loan portfolio
Risk category
Total loans	335,693	269,705
Consumer | Non-PCI loans | Other loan portfolio | Performing
Risk category
Total loans	335,439	269,492
Consumer | Non-PCI loans | Other loan portfolio | Impaired
Risk category
Total loans	254	213
Lease financing | Other loan portfolio
Risk category
Total loans	202,001	191,479
Lease financing | Non-PCI loans | Other loan portfolio
Risk category
Total loans	202,001	191,479
Lease financing | Non-PCI loans | Other loan portfolio | Performing
Risk category
Total loans	201,149	190,148
Lease financing | Non-PCI loans | Other loan portfolio | Impaired
Risk category
Total loans	$ 852	$ 1,331