FAIR VALUE OF FINANCIAL INSTRUMENTS (Assets and Liabilities Measured on a Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—trading	$ 25,097		$ 24,980
Securities—available-for-sale	3,275,979		2,322,593
Advances from FHLB	100,000		150,000
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—available-for-sale	3,275,979		2,322,593
Total assets	3,377,248		2,525,834
Junior subordinated debentures net of unamortized deferred issuance costs at fair value	117,520		116,974
Total liabilities	134,424		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	3,372		39,066
Derivative liabilities	438		22,336
Recurring [Member] | Interest rate swaps [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	28,038		5,641
Derivative liabilities	16,466		1,755
Recurring [Member] | U.S. Government and agency obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—available-for-sale	95,102		141,735
Recurring [Member] | Municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—available-for-sale	328,666		303,518
Recurring [Member] | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—available-for-sale	272,076		221,769
Recurring [Member] | TPS and TRUP CDOs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—trading	25,097		24,980
Recurring [Member] | Mortgage-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—available-for-sale	2,501,497		1,646,152
Recurring [Member] | Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—available-for-sale	78,638		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	44,762		133,554
Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
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]
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]
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]
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]
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]
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]
Securities—available-for-sale	3,275,979		2,322,593
Total assets	3,349,577		2,495,633
Junior subordinated debentures net of unamortized deferred issuance costs at fair value	0		0
Total liabilities	16,904		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	798		39,066
Derivative liabilities	438		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	28,038		420
Derivative liabilities	16,466		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]
Securities—available-for-sale	95,102		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]
Securities—available-for-sale	328,666		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]
Securities—available-for-sale	272,076		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]
Securities—available-for-sale	2,501,497		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]
Securities—available-for-sale	78,638		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	44,762		133,554
Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities—available-for-sale	0		0
Total assets	27,671		30,201
Junior subordinated debentures net of unamortized deferred issuance costs at fair value	117,520		116,974
Total liabilities	117,520		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	2,574		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	$ 2,937	5,221	$ 5,816	$ 2,517	$ 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]
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]
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]
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	25,097		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]
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]
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