CREDIT QUALITY ASSESSMENT - Credit Quality of Loan Portfolio, New (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Past Due [Line Items]
Past due		$ 27,748
Non-accrual loans		38,632
Loans greater than 90 days past due		0
Restructured loans		2,636
Total	$ 10,400,509	6,705,232
Performing loans:
Financing Receivable, Past Due [Line Items]
Current	10,226,191
Total performing loans	10,285,057
Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	112,361
Loans greater than 90 days past due	774
Restructured loans	2,317
Total non-performing loans	115,452
30-59 days
Financing Receivable, Past Due [Line Items]
Past due		19,986
30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	46,812
60-89 days
Financing Receivable, Past Due [Line Items]
Past due		7,762
60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	12,054
Commercial investor real estate
Financing Receivable, Past Due [Line Items]
Total	3,634,720
Commercial owner-occupied real estate
Financing Receivable, Past Due [Line Items]
Total	1,642,216
Commercial AD&C
Financing Receivable, Past Due [Line Items]
Total	1,050,973
Residential mortgage
Financing Receivable, Past Due [Line Items]
Total	1,105,179
Residential construction
Financing Receivable, Past Due [Line Items]
Total	182,619
Commercial real estate: | Commercial investor real estate
Financing Receivable, Past Due [Line Items]
Past due		932
Non-accrual loans		8,437
Loans greater than 90 days past due		0
Restructured loans		775
Total	3,634,720	2,169,156
Commercial real estate: | Commercial investor real estate | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	3,571,184
Total performing loans	3,589,360
Commercial real estate: | Commercial investor real estate | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	45,227
Loans greater than 90 days past due	133
Restructured loans	0
Total non-performing loans	45,360
Commercial real estate: | Commercial investor real estate | 30-59 days
Financing Receivable, Past Due [Line Items]
Past due		932
Commercial real estate: | Commercial investor real estate | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	14,046
Commercial real estate: | Commercial investor real estate | 60-89 days
Financing Receivable, Past Due [Line Items]
Past due		0
Commercial real estate: | Commercial investor real estate | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	4,130
Commercial real estate: | Commercial owner-occupied real estate
Financing Receivable, Past Due [Line Items]
Past due		316
Non-accrual loans		4,148
Loans greater than 90 days past due		0
Restructured loans		0
Total	1,642,216	1,288,677
Commercial real estate: | Commercial owner-occupied real estate | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	1,624,265
Total performing loans	1,630,655
Commercial real estate: | Commercial owner-occupied real estate | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	11,561
Loans greater than 90 days past due	0
Restructured loans	0
Total non-performing loans	11,561
Commercial real estate: | Commercial owner-occupied real estate | 30-59 days
Financing Receivable, Past Due [Line Items]
Past due		316
Commercial real estate: | Commercial owner-occupied real estate | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	6,390
Commercial real estate: | Commercial owner-occupied real estate | 60-89 days
Financing Receivable, Past Due [Line Items]
Past due		0
Commercial real estate: | Commercial owner-occupied real estate | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	0
Commercial real estate: | Commercial AD&C
Financing Receivable, Past Due [Line Items]
Past due		0
Non-accrual loans		829
Loans greater than 90 days past due		0
Restructured loans		0
Total	1,050,973	684,010
Commercial real estate: | Commercial AD&C | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	1,033,057
Total performing loans	1,035,929
Commercial real estate: | Commercial AD&C | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	15,044
Loans greater than 90 days past due	0
Restructured loans	0
Total non-performing loans	15,044
Commercial real estate: | Commercial AD&C | 30-59 days
Financing Receivable, Past Due [Line Items]
Past due		0
Commercial real estate: | Commercial AD&C | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	29
Commercial real estate: | Commercial AD&C | 60-89 days
Financing Receivable, Past Due [Line Items]
Past due		0
Commercial real estate: | Commercial AD&C | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	2,843
Commercial Business
Financing Receivable, Past Due [Line Items]
Non-accrual loans		8,450
Loans greater than 90 days past due		0
Restructured loans		417
Total	8,595,457	4,942,862
Commercial Business | Commercial business
Financing Receivable, Past Due [Line Items]
Past due		1,278
Non-accrual loans		8,450
Total	2,267,548	801,019
Commercial Business | Commercial business | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	2,238,617
Total performing loans	2,243,739
Commercial Business | Commercial business | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	22,933
Loans greater than 90 days past due	161
Restructured loans	715
Total non-performing loans	23,809
Commercial Business | Commercial business | 30-59 days
Financing Receivable, Past Due [Line Items]
Past due		908
Commercial Business | Commercial business | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	4,859
Commercial Business | Commercial business | 60-89 days
Financing Receivable, Past Due [Line Items]
Past due		370
Commercial Business | Commercial business | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	263
Residential real estate: | Residential mortgage
Financing Receivable, Past Due [Line Items]
Past due		19,394
Non-accrual loans		12,661
Loans greater than 90 days past due		0
Restructured loans		1,080
Total	1,105,179	1,149,327
Residential real estate: | Residential mortgage | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	1,073,963
Total performing loans	1,092,885
Residential real estate: | Residential mortgage | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	10,212
Loans greater than 90 days past due	480
Restructured loans	1,602
Total non-performing loans	12,294
Residential real estate: | Residential mortgage | 30-59 days
Financing Receivable, Past Due [Line Items]
Past due		14,853
Residential real estate: | Residential mortgage | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	16,213
Residential real estate: | Residential mortgage | 60-89 days
Financing Receivable, Past Due [Line Items]
Past due		4,541
Residential real estate: | Residential mortgage | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	2,709
Residential real estate: | Residential construction
Financing Receivable, Past Due [Line Items]
Past due		1,614
Non-accrual loans		0
Loans greater than 90 days past due		0
Restructured loans		0
Total	182,619	146,279
Residential real estate: | Residential construction | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	182,557
Total performing loans	182,619
Residential real estate: | Residential construction | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	0
Loans greater than 90 days past due	0
Restructured loans	0
Total non-performing loans	0
Residential real estate: | Residential construction | 30-59 days
Financing Receivable, Past Due [Line Items]
Past due		280
Residential real estate: | Residential construction | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	0
Residential real estate: | Residential construction | 60-89 days
Financing Receivable, Past Due [Line Items]
Past due		1,334
Residential real estate: | Residential construction | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	62
Consumer
Financing Receivable, Past Due [Line Items]
Past due		4,214
Non-accrual loans		4,107
Loans greater than 90 days past due		0
Restructured loans		364
Total	517,254	466,764
Consumer | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	502,548
Total performing loans	509,870
Consumer | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	7,384
Loans greater than 90 days past due	0
Restructured loans	0
Total non-performing loans	7,384
Consumer | 30-59 days
Financing Receivable, Past Due [Line Items]
Past due		2,697
Consumer | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	5,275
Consumer | 60-89 days
Financing Receivable, Past Due [Line Items]
Past due		$ 1,517
Consumer | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	$ 2,047