CREDIT QUALITY ASSESSMENT - Credit Quality of Loan Portfolio, New (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Total	$ 10,092,515	$ 10,400,509
Performing loans:
Financing Receivable, Past Due [Line Items]
Current	9,954,983	10,226,191
Total performing loans	9,998,208	10,285,057
Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	91,399	112,361
Loans greater than 90 days past due	680	774
Restructured loans	2,228	2,317
Total non-performing loans	94,307	115,452
30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	34,499	46,812
60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	8,726	12,054
Commercial investor real estate
Financing Receivable, Past Due [Line Items]
Total	3,712,374	3,634,720
Commercial owner-occupied real estate
Financing Receivable, Past Due [Line Items]
Total	1,687,843	1,642,216
Commercial AD&C
Financing Receivable, Past Due [Line Items]
Total	1,126,960	1,050,973
Residential mortgage
Financing Receivable, Past Due [Line Items]
Total	960,527	1,105,179
Residential construction
Financing Receivable, Past Due [Line Items]
Total	172,869	182,619
Commercial real estate: | Commercial investor real estate
Financing Receivable, Past Due [Line Items]
Total	3,712,374	3,634,720
Commercial real estate: | Commercial investor real estate | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	3,654,645	3,571,184
Total performing loans	3,670,302	3,589,360
Commercial real estate: | Commercial investor real estate | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	42,072	45,227
Loans greater than 90 days past due	0	133
Restructured loans	0	0
Total non-performing loans	42,072	45,360
Commercial real estate: | Commercial investor real estate | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	10,608	14,046
Commercial real estate: | Commercial investor real estate | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	5,049	4,130
Commercial real estate: | Commercial owner-occupied real estate
Financing Receivable, Past Due [Line Items]
Total	1,687,843	1,642,216
Commercial real estate: | Commercial owner-occupied real estate | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	1,670,611	1,624,265
Total performing loans	1,679,660	1,630,655
Commercial real estate: | Commercial owner-occupied real estate | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	8,183	11,561
Loans greater than 90 days past due	0	0
Restructured loans	0	0
Total non-performing loans	8,183	11,561
Commercial real estate: | Commercial owner-occupied real estate | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	8,874	6,390
Commercial real estate: | Commercial owner-occupied real estate | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	175	0
Commercial real estate: | Commercial AD&C
Financing Receivable, Past Due [Line Items]
Total	1,126,960	1,050,973
Commercial real estate: | Commercial AD&C | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	1,111,398	1,033,057
Total performing loans	1,112,471	1,035,929
Commercial real estate: | Commercial AD&C | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	14,489	15,044
Loans greater than 90 days past due	0	0
Restructured loans	0	0
Total non-performing loans	14,489	15,044
Commercial real estate: | Commercial AD&C | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	1,073	29
Commercial real estate: | Commercial AD&C | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	0	2,843
Commercial Business
Financing Receivable, Past Due [Line Items]
Total	8,501,543	8,595,457
Commercial Business | Commercial business
Financing Receivable, Past Due [Line Items]
Total	1,974,366	2,267,548
Commercial Business | Commercial business | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	1,961,950	2,238,617
Total performing loans	1,964,277	2,243,739
Commercial Business | Commercial business | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	9,435	22,933
Loans greater than 90 days past due	0	161
Restructured loans	654	715
Total non-performing loans	10,089	23,809
Commercial Business | Commercial business | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	980	4,859
Commercial Business | Commercial business | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	1,347	263
Residential real estate: | Residential mortgage
Financing Receivable, Past Due [Line Items]
Total	960,527	1,105,179
Residential real estate: | Residential mortgage | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	939,365	1,073,963
Total performing loans	948,833	1,092,885
Residential real estate: | Residential mortgage | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	9,440	10,212
Loans greater than 90 days past due	680	480
Restructured loans	1,574	1,602
Total non-performing loans	11,694	12,294
Residential real estate: | Residential mortgage | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	8,577	16,213
Residential real estate: | Residential mortgage | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	891	2,709
Residential real estate: | Residential construction
Financing Receivable, Past Due [Line Items]
Total	172,869	182,619
Residential real estate: | Residential construction | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	170,078	182,557
Total performing loans	172,807	182,619
Residential real estate: | Residential construction | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	62	0
Loans greater than 90 days past due	0	0
Restructured loans	0	0
Total non-performing loans	62	0
Residential real estate: | Residential construction | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	2,729	0
Residential real estate: | Residential construction | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	0	62
Consumer
Financing Receivable, Past Due [Line Items]
Total	457,576	517,254
Consumer | Performing loans:
Financing Receivable, Past Due [Line Items]
Current	446,936	502,548
Total performing loans	449,858	509,870
Consumer | Non-performing loans:
Financing Receivable, Past Due [Line Items]
Non-accrual loans	7,718	7,384
Loans greater than 90 days past due	0	0
Restructured loans	0	0
Total non-performing loans	7,718	7,384
Consumer | 30-59 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	1,658	5,275
Consumer | 60-89 days | Performing loans:
Financing Receivable, Past Due [Line Items]
Past due	$ 1,264	$ 2,047