INCOME TAXES - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Contingency [Line Items]
Maximum corporate tax rate	37.50%	37.50%	37.50%
Net deferred tax asset	$ 208,482	$ 329,261
Deferred tax asset related to NOLs	66,300
Valuation allowance	107,323	101,984
Deferred tax asset not subject to expiration period		210,700
Income tax expense	146,792	14,050	$ 71,995
UTBs	1,300
U S [Member]
Income Tax Contingency [Line Items]
Income tax expense	6,800	4,900	$ 4,500
UTBs	1,100
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	200
FirstBank [Member]
Income Tax Contingency [Line Items]
Valuation allowance	69,700
Holding Company and First Management [Member]
Income Tax Contingency [Line Items]
Valuation allowance	37,600
Subsidiaries [Member]
Income Tax Contingency [Line Items]
Net deferred tax asset	208,400	329,100
Valuation allowance	69,700	59,900
Deferred tax asset not subject to expiration period	$ 177,900	$ 210,700
Domestic Country [Member] | Subsidiaries [Member]
Income Tax Contingency [Line Items]
Dividend received deduction	100.00%
Domestic Country [Member] | Other taxable domestic corporations [Member]
Income Tax Contingency [Line Items]
Dividend received deduction	85.00%