FAIR VALUE OF FINANCIAL INSTRUMENTS (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—trading	$ 26,875		$ 24,980
Debt Securities, Available-for-sale	3,446,575		2,322,593
Advances from FHLB	50,000		150,000
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	3,446,575		2,322,593
Total assets	3,542,866		2,525,834
Junior subordinated debentures net of unamortized deferred issuance costs at fair value	124,853		116,974
Total liabilities	140,539		141,065
Recurring [Member] | Interest rate lock and forward sale commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	2,309		39,066
Derivative liabilities	136		22,336
Recurring [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	25,627		5,641
Derivative liabilities	15,550		1,755
Recurring [Member] | U.S. Government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	181,052		141,735
Recurring [Member] | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	310,391		303,518
Recurring [Member] | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	164,244		221,769
Recurring [Member] | TPS and TRUP CDOs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—trading	26,875		24,980
Recurring [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	2,584,264		1,646,152
Recurring [Member] | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	206,624		9,419
Recurring [Member] | Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Fair Value Disclosure	41,480		133,554
Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Total assets	0		0
Junior subordinated debentures net of unamortized deferred issuance costs at fair value	0		0
Total liabilities	0		0
Recurring [Member] | Level 1 [Member] | Interest rate lock and forward sale commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0		0
Derivative liabilities	0		0
Recurring [Member] | Level 1 [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0		0
Derivative liabilities	0		0
Recurring [Member] | Level 1 [Member] | U.S. Government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Level 1 [Member] | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Level 1 [Member] | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Level 1 [Member] | TPS and TRUP CDOs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—trading	0		0
Recurring [Member] | Level 1 [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Level 1 [Member] | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Level 1 [Member] | Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Fair Value Disclosure	0		0
Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	3,446,575		2,322,593
Total assets	3,514,596		2,495,633
Junior subordinated debentures net of unamortized deferred issuance costs at fair value	0		0
Total liabilities	15,686		24,091
Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest rate lock and forward sale commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	914		39,066
Derivative liabilities	136		22,336
Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	25,627		420
Derivative liabilities	15,550		1,755
Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	181,052		141,735
Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	310,391		303,518
Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	164,244		221,769
Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | TPS and TRUP CDOs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—trading	0		0
Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	2,584,264		1,646,152
Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	206,624		9,419
Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Fair Value Disclosure	41,480		133,554
Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Total assets	28,270		30,201
Junior subordinated debentures net of unamortized deferred issuance costs at fair value	124,853		116,974
Total liabilities	124,853		116,974
Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest rate lock and forward sale commitments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	1,395		0
Derivative liabilities	0		0
Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0	$ 2,574	5,221	$ 8,454	$ 5,816	$ 791
Derivative liabilities	0		0
Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | TPS and TRUP CDOs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—trading	26,875		24,980
Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale	0		0
Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans Held-for-sale, Fair Value Disclosure	$ 0		$ 0