INCOME TAXES - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Tax Contingency [Line Items]
Minimum percentage of bank net taxable income for paying Income tax at normal rate	20.00%
Income tax expense	$ 17,618	$ 7,758
Estimated annual effective tax rate excluding entities from which a tax benefit cannot be recognized and discrete items	28.00%	27.00%
Effective Income Tax Rate Continuing Operations	29.00%	19.00%
Effective Income Tax Rate Excluding Discrete Items	26.00%	23.00%
Deferred Tax Assets Net	$ 306,000
Valuation allowance	95,600
United States [Member]
Income Tax Contingency [Line Items]
Foreign Income Tax Expense (Benefit), Continuing Operations	1,000	$ 1,600
FirstBank [Member]
Income Tax Contingency [Line Items]
Deferred Tax Assets Net	305,900		$ 319,800
Valuation allowance	$ 63,500		$ 68,100
Domestic Tax Authority [Member] | Other taxable domestic corporations [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%