INCOME TAXES - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Income Tax Contingency [Line Items]
Effective tax rate maximum statutory rate			37.50%
Minimum percentage of bank net taxable income for paying Income tax at normal rate			20.00%
Income tax expense (benefit)	$ 6,046	$ 18,011	$ 3,079	$ 35,629
Estimated annual effective tax rate, excluding entities from which a tax benefit cannot be recognized and discrete items			25.00%	29.00%
Estimated annual effective tax rate, including all entities			27.00%	29.00%
Effective Income Tax Rate Excluding Discrete Items			27.00%	30.00%
Deferred Tax Assets Net Increase Decrease			$ 31,300
Deferred Tax Assets Net	306,200		306,200
Valuation allowance	87,300		87,300
COVID-19
Income Tax Contingency [Line Items]
Income tax expense (benefit)	(9,900)		(29,900)
United States [Member]
Income Tax Contingency [Line Items]
Income tax expense (benefit)	1,200	$ 1,200	2,200	$ 2,200
FirstBank [Member]
Income Tax Contingency [Line Items]
Deferred Tax Assets Net	306,000		306,000		$ 264,800
Valuation allowance	$ 50,800		$ 50,800		$ 55,600
Domestic Tax Authority [Member] | Other taxable domestic corporations member [Member]
Income Tax Contingency [Line Items]
Dividend received deduction			85.00%
Domestic Tax Authority [Member] | Subsidiaries [Member]
Income Tax Contingency [Line Items]
Dividend received deduction			100.00%