SEGMENT REPORTING - Schedule of Segment Reporting, by Reportable Business Segments (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Segment Reporting Information [Line Items]
Interest income	$ 79,512	$ 67,050
Interest expense	10,711	6,460
Net interest income	68,801	60,590
Provision for loan losses	1,801	1,836	$ 8,364
Noninterest income	26,464	25,706
Noninterest expense
Salaries and employee benefits	32,089	27,794
Equipment and occupancy expenses	6,198	5,877
Data processing and telecommunications expenses	7,135	6,572
Other expenses	13,676	12,850
Total noninterest expense	59,098	53,093
Income before income tax expense	34,366	31,367
Income tax expense	7,706	10,214
Net income	26,660	21,153
Total assets	8,022,828	7,094,856	7,856,203
Goodwill	208,513	125,532	125,532
Other intangible assets, net	12,562	16,391	$ 13,496
Banking Division
Segment Reporting Information [Line Items]
Interest income	60,896	54,212
Interest expense	5,537	4,086
Net interest income	55,359	50,126
Provision for loan losses	888	1,982
Noninterest income	13,099	13,013
Noninterest expense
Salaries and employee benefits	22,068	18,844
Equipment and occupancy expenses	5,477	5,257
Data processing and telecommunications expenses	6,304	6,043
Other expenses	11,080	9,241
Total noninterest expense	44,929	39,385
Income before income tax expense	22,641	21,772
Income tax expense	5,242	6,856
Net income	17,399	14,916
Total assets	6,464,130	6,100,876
Goodwill	125,532	125,532
Other intangible assets, net	12,562	16,391
Retail Mortgage Division
Segment Reporting Information [Line Items]
Interest income	6,822	4,054
Interest expense	1,825	1,078
Net interest income	4,997	2,976
Provision for loan losses	217	8
Noninterest income	11,585	10,513
Noninterest expense
Salaries and employee benefits	7,742	7,216
Equipment and occupancy expenses	593	519
Data processing and telecommunications expenses	389	317
Other expenses	1,731	1,141
Total noninterest expense	10,455	9,193
Income before income tax expense	5,910	4,288
Income tax expense	1,244	1,501
Net income	4,666	2,787
Total assets	613,706	378,897
Goodwill	0	0
Other intangible assets, net	0	0
Warehouse Lending Division
Segment Reporting Information [Line Items]
Interest income	2,752	1,333
Interest expense	897	228
Net interest income	1,855	1,105
Provision for loan losses	0	(232)
Noninterest income	397	319
Noninterest expense
Salaries and employee benefits	138	147
Equipment and occupancy expenses	0	1
Data processing and telecommunications expenses	33	27
Other expenses	52	32
Total noninterest expense	223	207
Income before income tax expense	2,029	1,449
Income tax expense	426	507
Net income	1,603	942
Total assets	247,257	107,937
Goodwill	0	0
Other intangible assets, net	0	0
SBA Division
Segment Reporting Information [Line Items]
Interest income	1,431	1,213
Interest expense	507	306
Net interest income	924	907
Provision for loan losses	537	48
Noninterest income	1,370	1,815
Noninterest expense
Salaries and employee benefits	740	591
Equipment and occupancy expenses	58	51
Data processing and telecommunications expenses	9	1
Other expenses	236	211
Total noninterest expense	1,043	854
Income before income tax expense	714	1,820
Income tax expense	150	637
Net income	564	1,183
Total assets	109,011	76,405
Goodwill	0	0
Other intangible assets, net	0	0
Premium Finance Division
Segment Reporting Information [Line Items]
Interest income	7,611	6,238
Interest expense	1,945	762
Net interest income	5,666	5,476
Provision for loan losses	159	30
Noninterest income	13	46
Noninterest expense
Salaries and employee benefits	1,401	996
Equipment and occupancy expenses	70	49
Data processing and telecommunications expenses	400	184
Other expenses	577	2,225
Total noninterest expense	2,448	3,454
Income before income tax expense	3,072	2,038
Income tax expense	644	713
Net income	2,428	1,325
Total assets	588,724	430,741
Goodwill	82,981	0
Other intangible assets, net	$ 0	$ 0