SUPPLEMENTAL CASH FLOW INFORMATION - Supplemental Cash Flow Information (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Sep. 01, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Cash paid for:
Interest on borrowings				$ 71,859	$ 79,789
Income tax				13,200	10,238
Operating cash flow from operating leases				8,492	7,619
Non-cash investing and financing activities:
Additions to OREO				6,608	29,670
Additions to auto and other repossessed assets				24,160	34,497
Capitalization of servicing assets		$ 1,598	$ 986	3,168	2,855
Loan securitizations				156,786	173,428
Loans held for investment transferred to held for sale				4,876	20,928
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability				1,328	8,139
Adoption of lease accounting standard:
Right-of-use assets operating leases		107,629		107,629		$ 61,327
Operating Lease, Liability		110,888		110,888		$ 64,259
Santander [Member]
Adoption of lease accounting standard:
Right-of-use assets operating leases	$ 52,100
Operating Lease, Liability	52,100
Acquisition
Total purchase price consideration (cash)	1,277,626
Total assets and identifiable intangible assets acquired	5,500,000
Santander [Member] | Fair Value
Acquisition
Total assets and identifiable intangible assets acquired	5,562,132
Total liabilities assumed	$ 4,290,809
ASU 2016-02 [Member]
Adoption of lease accounting standard:
Right-of-use assets operating leases		0	57,178	0	57,178
Operating Lease, Liability		$ 0	$ 59,818	$ 0	$ 59,818