CREDIT QUALITY ASSESSMENT (Credit Risk Rating Indicators for Each Segment of Commercial Loan Portfolio) (Detail) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 10,333,935	$ 6,705,232
Commercial Loan
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		4,942,862
Pass
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		4,892,398
Special Mention
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		7,960
Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		42,504
Doubtful
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	3,588,702	2,169,156
Commercial real estate: | Commercial owner-occupied real estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	1,652,208	1,288,677
Commercial real estate: | Commercial AD&C
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	994,800	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	8,462,956	4,942,862
Commercial Business | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans	$ 2,227,246	801,019
Commercial Business | Pass | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		783,909
Commercial Business | Special Mention | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		2,487
Commercial Business | Substandard | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		14,623
Commercial Business | Doubtful | Commercial business
Financing Receivable, Credit Quality Indicator [Line Items]
Total loans		$ 0