CREDIT QUALITY ASSESSMENT - Credit Risk Rating Indicators for Each Segment of Commercial Loan Portfolio (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 10,400,509	$ 6,705,232
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		4,942,862
Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,634,720
Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,642,216
Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,050,973
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		4,892,398
Pass | Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,571,736
Pass | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,611,009
Pass | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,030,273
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		7,960
Special Mention | Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	17,052
Special Mention | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	14,272
Special Mention | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,711
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		42,504
Substandard | Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	45,932
Substandard | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	16,703
Substandard | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	18,989
Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		0
Doubtful | Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0
Doubtful | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	232
Doubtful | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	0
Commercial real estate: | Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	3,634,720	2,169,156
Commercial real estate: | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,642,216	1,288,677
Commercial real estate: | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,050,973	684,010
Commercial real estate: | Pass | Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		2,146,971
Commercial real estate: | Pass | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		1,278,337
Commercial real estate: | Pass | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		683,181
Commercial real estate: | Special Mention | Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		3,189
Commercial real estate: | Special Mention | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		2,284
Commercial real estate: | Special Mention | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		0
Commercial real estate: | Substandard | Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		18,996
Commercial real estate: | Substandard | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		8,056
Commercial real estate: | Substandard | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		829
Commercial real estate: | Doubtful | Commercial investor real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		0
Commercial real estate: | Doubtful | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		0
Commercial real estate: | Doubtful | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		0
Commercial Business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	8,595,457	4,942,862
Commercial Business | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,267,548	801,019
Commercial Business | Pass | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	2,228,469	783,909
Commercial Business | Special Mention | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	10,387	2,487
Commercial Business | Substandard | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	20,658	14,623
Commercial Business | Doubtful | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 8,034	$ 0