SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) segment rating shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Cash and Cash Equivalents
Restricted cash	$ 43,000	$ 0
Other Investments
Held-to-maturity securities	79,900	0
Other investments	47,552	28,202
Servicing Rights
Servicing fees	56,000	37,200	$ 19,900
Allowance for Credit Losses
Deferred interest on financing receivable allowance for credit losses	$ 214	718
Number of risk ratings | rating	9
Number of risk ratings, pass | rating	5
Number of risk ratings, criticized | rating	4
Leases
Initial lease terms	13 years
Share-based Compensation
Company stock-based compensation cost	$ 7,900	$ 3,900	$ 3,400
Earnings Per Share
Anti-dilutive common shares excluded (in shares) | shares	0	197,765	0
Mortgage Banking Derivatives
Fair value of derivative instruments, asset	$ 11,900	$ 51,800
Fair value of derivative instruments, liability	$ 710	16,400
Operating Segments
Number of reportable segments | segment	5
Minimum | Core deposit premiums
Goodwill and Intangible Assets
Acquired finite-lived intangible assets, weighted average useful life	7 years
Maximum | Core deposit premiums
Goodwill and Intangible Assets
Acquired finite-lived intangible assets, weighted average useful life	10 years
Financing receivable
Other Investments
Interest receivable	$ 54,800	73,400
Allowance for Credit Losses
Interest receivable	54,800	73,400
Available-for-sale Securities
Other Investments
Interest receivable	2,400	3,600
Allowance for Credit Losses
Interest receivable	$ 2,400	$ 3,600
Buildings and leasehold improvements | Maximum
Premises and Equipment
Estimated useful lives, premises and equipment	40 years
Furniture and equipment | Minimum
Premises and Equipment
Estimated useful lives, premises and equipment	3 years
Furniture and equipment | Maximum
Premises and Equipment
Estimated useful lives, premises and equipment	20 years
Software And Computer Equipment | Minimum
Premises and Equipment
Estimated useful lives, premises and equipment	3 years
Software And Computer Equipment | Maximum
Premises and Equipment
Estimated useful lives, premises and equipment	5 years
US Premium Financing Holding Company | Minimum | Referral relationships
Goodwill and Intangible Assets
Acquired finite-lived intangible assets, weighted average useful life	8 years
US Premium Financing Holding Company | Minimum | Trade names
Goodwill and Intangible Assets
Acquired finite-lived intangible assets, weighted average useful life	5 years
US Premium Financing Holding Company | Minimum | Non-compete agreements
Goodwill and Intangible Assets
Acquired finite-lived intangible assets, weighted average useful life	3 years
US Premium Financing Holding Company | Maximum | Referral relationships
Goodwill and Intangible Assets
Acquired finite-lived intangible assets, weighted average useful life	10 years
US Premium Financing Holding Company | Maximum | Trade names
Goodwill and Intangible Assets
Acquired finite-lived intangible assets, weighted average useful life	7 years
US Premium Financing Holding Company | Maximum | Non-compete agreements
Goodwill and Intangible Assets
Acquired finite-lived intangible assets, weighted average useful life	10 years
Visa Class B Shares
Other Investments
Shares held in other investment (in shares) | shares	57,611
Other investments	$ 242
Conversation ratio	1.6181